Fast attack craft: the origins

by Chris Chant on 06/06/2011

A grey fast attack craft of the the German navy, moored next to others,  with German flag at the prowMany of the world’s navies, including a large number without any claim to a long-standing naval or even maritime tradition, operate forces of small but comparatively heavily armed fast combat craft. These can be defined as vessels with a displacement of up to 600 tons and a speed of 25 kt or more, and fall into two basic categories. These are the fast patrol boat (FPB) and the fast attack craft (FAC). The FPB is generally fitted with only light armament (generally machine guns and cannon of up to 40-mm calibre) together with minimal sensor and fire-control suites. The FAC is a considerably more formidable type usually capable of higher speeds and carrying a heavier, longer-ranged armament that can include anti-ship guided missiles, guns of up to 3-in (76-mm) calibre, heavyweight anti-ship torpedoes of up to 21-in (533-mm) calibre, and anti-submarine weapons such as lightweight homing torpedoes, rocket-propelled grenades and depth charges, all controlled with the aid of a considerably more sophisticated sensor and fir-control suites.

The nature of the primary armament is generally indicated by a suffixed letter: thus the FAC(G) carries a medium-calibre gun, the FAC(M) carries anti-ship missiles, the FAC(T) carries anti-ship torpedoes etc.

The FPB is considerably inferior to the FAC in combat capability, but is still worthy of examination. Many countries use such FPBs for patrol and protection of their territorial waters and associated economic zones, which have acquired considerably greater importance in recent years as resources such as oil and gas have been discovered in such areas. In times of peace, therefore, the FPB has an important role as a type of maritime policeman that can also be used for rescue and other humanitarian purposes. Many such FPBs have been designed with upgrading in mind, however, and in times of crisis can be converted into FACs by the addition of items such as heavier armament (usually anti-ship missiles and/or a medium-calibre guns) and a more capable fire-control system.

The most important weapon carried by the FAC is the anti-ship missile, which is now a light and compact weapon carrying a potent warhead over a usefully long range with devastating accuracy. The modern anti-ship missile can destroy a major warship with a single round, as demonstrated during the Falklands war of 1982, when a French-supplied Aérospatiale Exocet (in this instance fired by a warplane though in its basic form it is a surface-launched weapon) devastated the British ‘Type 42’ class destroyer Sheffield. The light weight and compact size of these missiles means that even small FACs can carry four such weapons, conferring virtual capital ship status on what is in effect a highly affordable craft.

A large part of the anti-ship missile’s capability rests with its advanced guidance, self-protection and attack electronics, which have benefited greatly from advances in electronics and electronic miniaturization in the last quarter of a century. Developments in electronics, including the use of digital in place of analog processing and computing techniques, have made the the guidance package considerably more capable, yet miniaturization techniques have allowed this package to be made smaller and lighter so that a missile of the same weight can carry either a greater fuel load or a larger warhead.

These electronic improvements have also transformed the capabilities of the launch vessel’s sensor and fire-control suites. Combined with advances in computing, this has allowed modern surveillance and tracking radars, optronic sensors, sonars, electronic warfare systems, action information systems, and fire-control systems to be fitted in small hulls that nonetheless carry potent long-range armament whose destructive capabilities are maximised by the launch vessel’s electronic systems. In this instance, small most certainly does mean beautiful, for it reduces procurement costs as an initial advantage and then contributes reduced manning and maintenance costs.

A similar advance has been made in propulsion, where the modern diesel engine is powerful yet notably compact and highly reliable, and is often used in conjunction with a gas turbine. The former has been developed in turbocharged form for great power and considerable economy of operation despite its small overall dimensions and comparatively low weight. The latter is also compact and light, yet offers a very high power/weight ratio at the expense of high fuel consumption. A combined propulsion arrangement therefore offers the power of the gas turbine for combat speed, and the economy of the diesel for long cruising endurance.

Recent developments have tended to obscure the fact that the FAC is not a wholly new development, but is a type with more than a century of pedigree behind it. The first small warship may be regarded as John I. Thornycroft’s torpedo boat Lightning built for the Royal Navy in 1876/77. About 10 years earlier Robert Whitehead had demonstrated the capabilities of his new invention, the self-propelled torpedo, and since that time Thornycroft had urged the Admiralty for permission to develop a torpedo-armed launch based on his successful series of fast steam launches. Displacing 32.5 tons and possessing an overall length of 87 ft (26.52 m), Lightning was powered by a compound steam engine delivering 460 ihp (343 kW) to one shaft for a speed of 19 kt, and had a complement of 15. As delivered, Lightning was fitted with two ‘torpedo frames’, which were torpedo-carrying cages that could be lowered into the water on either side of the launch before the torpedo was released for its free-running attack. These frames could not be used when the launch was moving at any speed, and in 1879 they were replaced by a torpedo tube mounted over the bow; two reload torpedoes were carried on trolleys either side amidships.

By the beginning of the 20th century, the Royal Navy alone had operated more than 100 such steam-powered boats. The later units displaced some 200 tons each and could reach 25 kt.

By World War I, there was already a division of torpedo boats into smaller attack craft (the torpedo boat) and slightly larger defensive craft (the torpedo boat destroyer), and this division increased during the war. The small torpedo boat virtually disappeared, and the torpedo boat destroyer emerged as the multi-role destroyer, a larger and far more capable type offering high speed together with a gun and torpedo armament. The original stream of small attack craft did not disappear entirely, however, for as late as 1918 the Germans were producing such craft. The vessels of the ‘A92’ class, for example, displaced 392 tons and had an overall length of 61.2 m (200.75 ft), and their geared steam turbines delivered 6,000 hp (4475 kW) to two shafts for a maximum speed of 26.7 kt; the armament comprised two 88-mm (3.46-in) guns and one 450-mm (17.7-in) torpedo tube.

The trouble with such torpedo boats, however, was that they were too small and vulnerable for fleet operations, and at the same time too large and unhandy for coastal operations against convoys escorted by destroyers. Thus the mantle of coastal operations, now firmly established as the metier of such torpedo boats, shifted onto the shoulders of the type of smaller craft made possible by the replacement of the steam powerplant by the internal combustion engine.

The main thrusting force in the development of such torpedo boats was the German navy. The ‘LM’ class units of 1917/18 each displaced between 15 and 17 tons and possessed an overall length of between 14.6 and 17.1 m (48 and 56 ft). Each unit was powered by three Maybach petrol engines delivering a total of between 630 and 720 hp (470 and 535 kW) to three shafts for a maximum speed of between 28 and 32 kt. The armament was a single 450-mm (17.7-mm) torpedo tube.

On the other side of the maritime front line, the British developed a similar though smaller type as the coastal motor boat (CMB) that entered service in 1916. The CMB was evolved from pre-war racing boats with a stepped hydroplaning hull that allowed speeds in excess of 40 kt. The type was too small and light to carry a torpedo tube, so the boats were armed with a single torpedo that was launched tail-first over a stern chute, the boat then having the agility to swerve out of the torpedo’s path as the latter accelerated along the boat’s original course. The boats were built in 40-, 55- and 70-ft (12.2-, 16.8- and 21.3-m) lengths, the most numerous being the 55-ft (16.8-m) type that was built in several forms with different engines and armaments. The typical 55-ft CMB had a displacement of 11 tons and an overall length of 60 ft (18.3 m) over the torpedo-launching chute. Two petrol engines delivered between 750 and 900 hp (560 and 670 kW) to two shafts for a maximum speed of between 34 and 42 kt. The armament comprised one or two 18-in (457-mm) torpedoes, four 0.303-in (7.7-mm) Lewis machine guns, and up to four depth charges.

The World War I combatant that made the greatest use of torpedo craft was Italy, which developed as built 422 craft of several MAS types. Though completed after the war, a class that typifies such Italian craft was the ‘D’ group of the SVAN Veloce type. Each unit displaced 28.9 tons and had an overall length of 22.0 m (72.2 ft). The propulsion arrangement comprised four Isotta-Fraschini petrol engines delivering 1,600 hp (1195 kW) to four shafts or two Rognini electric motors delivering 10 hp (7.5 kW) to two shafts for silent approach, and the maximum speeds of these two arrangements were 30 kt and 4 kt respectively. The armament comprised two 450-mm (17.7-in) torpedoes, two 6.5-mm (0.26-in) machine guns and up to 20 depth charges. Two of these MAS boats showed the potential of small attack craft by torpedoing and sinking Wien, a pre-dreadnought battleship of the Austro-Hungarian navy.

During the 1920s, the concept of such coastal torpedo craft fell into disfavour, and it was only during the later 1930s that there was something of a revival. It was Germany that effectively pioneered the renaissance with S 1 of 1929, designed and built by Lürssen of Vegesack as the prototype of the new Schnellboote (fast boats) that came to be called E-boats by the Allies. The boats were based on a round-bilge rather than hard-chine hull for improved seaworthiness. S 1 displaced 51.5 tons and had an overall length of 27.0 m (88.5 ft). The propulsion arrangement comprised three Daimler-Benz petrol engines delivering 3,300 hp (2460 kW) to three shafts for a maximum speed of 34 kt, and the armament included one 20-mm cannon and two tubes for 500-mm (19.7-mm) torpedoes. S 1 proved seaworthy and effective, but serious doubts were raised about its propulsion arrangement, whose petrol engines provided shorter range than diesel units and whose fuel was known to be dangerously flammable. This last became of particular concern, for the boat lacked armour protection and would therefore be highly vulnerable to the fire that might follow hits from conventional rounds, let alone incendiary projectiles.

S 6 therefore introduced the diesel-engined powerplant that remained standard in all Schnellboote up to the end of World War II. S 7 introduced the distinctive knuckled hull form, and S 18 introduced the Daimler-Benz diesel that was used in all later boats. Later boats had a raised forecastle over the torpedo tubes, and reload torpedoes were carried aft. During World War II, gun armament was increased significantly, and the Schnellboote matured as exceptional fast combat craft. Lürssen built 162 Schnellboote during World War II, and other yards produced about the same number to the basic Lürssen design. The craft were extensively used in the North Sea and Baltic Sea, but their undoubted technical merits were not matched by aggressive leadership, so their effect was less than that of the smaller and less capable British craft, which were handled with considerably greater flair.

During the war, the displacement of the ‘average’ Schnellboot increased from 35 to 105 tons, the length from 28.0 to 34.9 m (91.9 to 114.5 ft), and the speed from 37 to 42 kt. Typical of the Schnellboot in its fully fledged form was the ‘S 186’ type built in 1944/45. This had a displacement of 105.5 tons and an overall length of 35.1 m (114.75 ft), and its propulsion arrangement was based on three Daimler-Benz diesels delivering 7,500 hp (5590 kW) to three shafts for a maximum speed of 41 kt. The armament included two 533-mm (21-in) tubes for four torpedoes, and two 30-mm cannon (fore and aft) often supplemented by numbers of lighter weapons.

The British returned to the concept of torpedo-armed coastal craft in 1935, when the Admiralty placed orders for motor torpedo boat (MTB) prototypes with the British Power Boat Company. These became the precursors of several important types, most notably the British motor gun boat (MGB) and American PT (pursuit torpedo) boat, but in the event most British MTBs were built to a baseline Vosper design of hard-chine form. This was enlarged during World War II and fitted with greater power and armament, but remained essentially unchanged. A notable feature of British MTB design in World War II was the frequent replacement of the 21-in (533-mm) heavyweight torpedo, of which only two could be shipped, by the 18-in (457-mm) medium-weight torpedo, of which four could be carried. In common with their German foes, the British crews added whatever gun armament they could to their fast combat craft as wartime experience revealed the need for additional cannon and machine gun armament for use against enemy surface craft and aircraft.

For lack of a suitable British engine, the Italian Isotta-Fraschini petrol engine was used in early craft until Italy’s June 1940 entry into the war on the Axis side cut off supplies. After a problem with the final drive had been eliminated, Packard engines from the USA then became the standard type for British craft. It was notable throughout the war, however, that the petrol-engined British craft were considerably more prone to fires than their diesel-engined German opponents.

Typical of the British MTB late in World War II was the Vosper 73-ft (22.25-m) type, which was authorised and built in 1944. This had a displacement of 46.7 tons and an overall length of 72 ft (22.3 m). The propulsion arrangement was three Packard petrol engines delivering 4,050 hp (3020 kW) to three shafts for a maximum speed of 39.5 kt, and the armament comprised four 18-in tubes for four torpedoes, two 20-mm cannon and four 0.303-in (7.7-mm) machine guns.

The ‘Fairmile D’ class also produced late in World War II was a larger and more capable design that could be completed as an MTB or MGB. The type had a displacement of 105 tons and an overall length of 115 ft (35.1 m). The propulsion arrangement comprised four Packard petrol engines delivering 5,000 hp (3730 kW) to four shafts for a maximum speed of 29 kt. The basic armament included one 2-pdr (40-mm) gun, two 20-mm cannon in a twin mounting, four 0.5-in (12.7-mm) machine guns in two twin mountings, and four 0.303-in machine guns in two twin mountings; later in the war, the 2-pdr gun was replaced by a 6-pdr (57-mm) weapon, a second weapon of the same type being located aft in place of the 20-mm twin mounting, which was moved farther forward. To this could be added two 21-in tubes for two torpedoes, though later in the war it was more common to see four 18-in tubes for four torpedoes.

The British also developed dedicated MGBs that complemented the MTBs in providing a balanced offensive capability. Here the primary designer and builder was the British Power Boat Company, which produced five basic classes. The largest of these classes was the ‘MGB-107’ type, of which 60 were built from 1942. This type had a displacement of 37 tons and an overall length of 71.75 ft (21.9 m). The propulsion arrangement comprised three Packard petrol engines delivering 4,050 hp (3020 kW) to three shafts for a maximum speed of 42 kt, and the armament included one 2-pdr gun, two 20-mm cannon in a twin mounting and four 0.303-in machine guns in two twin mountings. In 1943 some of the craft were converted into hybrid MTB/MGB types with two 18-in tubes for two torpedoes, and some of the craft were completed to this standard.

Early experience with the MTB and MGB showed the British that a large measure of the tactical surprise could be secured by the types’ high speed and small silhouette, but that this element of surprise was often lost because of the two types’ great noise, which resulted from the use of unsilenced engines. In the longer term, the answer was found to lie in an effective silencing system. In the shorter term, however, the British tried to develop a quieter type with steam propulsion. The resulting steel-hulled steam gun boat (SGB) was a large round-bilge type that was both fast and quiet. On the other side of the coin, however, its machinery was also extremely vulnerable to damage from even the lightest of gunfire and its production could only be undertaken at the expense of the construction of larger warships such as destroyers, frigates, corvettes and sloops.

Plans were laid for 60 SGBs, but in the event only nine were ordered and seven actually built. To provide protection for their vulnerable machinery, the boats were fitted with 0.75-in (19-mm) armour over their machinery spaces, and the weight of this metal reduced speed dramatically. The SGB displaced 165 tons and had an overall length of 145.25 ft (44.3 m). The propulsion arrangement comprised geared steam turbines delivering 8,000 hp (5965 kW) to two shafts for a maximum speed of 35 kt, and the armament included two 2-pdr guns in single mountings, four 0.5-in machine guns in two twin mountings, and two 21-in tubes for two torpedoes. The gun armament was later strengthened to one 3-in (76-mm) gun, two 6-pdr guns in single mountings and six 20-mm cannon in three twin mountings, which required the complement to be increased from 27 to 34. Together with the armour, this raised displacement to 260 tons and reduced speed to 30 kt.

The US Navy showed very little interest in fast combat craft of such coastal types until 1939, when contracts were placed with six yards, including the British Power Boat Company, for prototype craft varying in length between 54 and 80 ft (16.5 and 24.4 m). The type that found greatest technical favour was that of the British Power Boats Company, and salient features of this design were incorporated in later American designs. Like the British craft, these US boats were of the hard-chine type, and more than 800 such craft were ordered before the end of World War II. The three main types were the ‘PT 71’ class ordered from Higgins Industries of New Orleans, Louisiana, the ‘PT 103’ class ordered from Elco (Electric Boat Company) of Bayonne, New Jersey, and the ‘PT 368’ class ordered from a number of smaller yards such as R. Jacobs, Herreshoff, the Annapolis Yacht Company, and Canadian Power Boats.

The ‘PT 71’ class displaced 46 tons and had an overall length of 78 ft (23.8 m). The propulsion arrangement comprised three Packard 4M2500 petrol engines delivering 4,050 hp (3020 kW) to three shafts for a maximum speed of 40+ kt, and the armament comprised two or four 21-in tubes for two or four torpedoes, one 40-mm gun, two 20-mm cannon, varying numbers of 0.5-in machine guns and, in two-tube craft, 12 depth charges or four mine racks. The ‘PT 103’ class displaced 45 tons and had an overall length of 80.3 ft (24.5 m). The propulsion arrangement again comprised three Packard 4M2500 petrol engines delivering 4,050 hp (3020 kW) to three shafts for a maximum speed of 40+ kt, and the armament comprised four 21-in tubes for four torpedoes, two 20-mm cannon and varying numbers of 0.5-in machine guns. The ‘PT 368’ class displaced 43 tons and had an overall length of 70 ft (21.3 m). The propulsion arrangement comprised the standard three Packard 4M2500 petrol engines delivering 4,050 hp (3020 kW) to three shafts for a maximum speed of 40+ kt, and the armament comprised two 21-in tubes for two torpedoes as well as varying numbers of 20-mm cannon and 0.5-in machine guns.

Like the Americans, the Japanese were late into the development of coastal craft. All Japanese craft of this type were developed from two British craft, Thornycroft-built CMBs including one captured at Canton in 1938. Examination of these two types resulted in a Japanese-designed experimental type built in 1940. This led to the construction of at least 248 MTBs before Japan’s defeat in 1945. Typical of these was the ‘Type T-14’ class, which had a displacement of 15 tons, a length of 15.0 m (49.2 ft), a propulsion arrangement of one Type 91 petrol engine delivering 920 hp (685 kW) for a maximum speed of 28 kt, and an armament of two 457-mm (18-in) tubes for two torpedoes as well as one 25-mm cannon or 13-mm (0.51-in) machine gun. In parallel with these small and highly limited MTBs, the Japanese also developed some MGBs. Typical of these was the ‘Type H-2’ class with a displacement of 24.5 tons, length of 18.0 m (59.1 ft), propulsion arrangement of two Type 11 petrol engines delivering 2,100 hp (1565 kW) to two shafts for a maximum speed of 33.5 kt, and armament of two 20-mm cannon, two 7.7-mm (0.303-in) machine guns and two depth charges. In overall terms, however, the Japanese MTBs and MGBs were a technical dead end.

After World War II, development of these fast combat craft came to a virtual end in the navies of the victorious western Allies. The UK and USA decided that their fast combat craft had played on a comparatively ineffective part on the naval effort of World War II, and that their navies should therefore return to the pre-war concept whose large surface combatants had dominated operations in the Atlantic and Pacific Oceans. Large numbers of fast combat craft were therefore deleted or transferred to smaller navies. These latter used the craft mainly for the patrol role, but the navies of some middle-rank nations used them as a sort of stepping stone toward the re-creation of conventional navies out of the ashes of World War II.

It is worth noting, however, that there were a number of interesting experimental developments in fast combat craft. The most important, one can now say with hindsight, was the re-engining of a British SGB with two Rolls-Royce RM.60 engines to create the world’s first vessel powered only by gas turbines.

[Photo by yetdark]

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