The British hard-chined Coastal Motor Boats of World War I were very fast but required constant attention to trim in order to get the best performance. 1919 saw them in use in a little-known campaign on the Caspian, during the intervention by the Western powers in Russia.
S12 and S13 were part of the first batch of German motor torpedo boats, completed in I 934. Displacing 78 tons, they were 32.3-m (l 06-ft) boats armed with two 533-mm (21-in) torpedoes and a single 20-mm (0.78-in)gun intended for an AA role.
Fast coastal craft proved their worth during World War I, with the Italians achieving the greatest successes, including the sinking of several battleships. In the inter-war years the larger fleets concentrated on major units and ignored coastal craft, but Germany and Italy continued their development, giving them a substantial lead by 1939.
Although the development of the automotive torpedo in the late 19th century promised to realize the dream of the small warship with the killer punch, the need for this ‘torpedo boat’ to work with and against fleets at sea stimulated too large an increase in size, a trend aggravated by the contemporary technology of steam machinery in displacement hulls. The development of the fast planing hull and the internal combustion engine began the cycle afresh, with progress before 1914 owing much to the commercial prospects of high-speed boating. It was but a small step to mount torpedoes on such craft, and the same specialist yards have tended to remain in the business to this day.
Much effort was put into the production of torpedo-carrying coastal craft during World War l, but only the Italians in the Adriatic and the British in the English Channel and the Baltic ever demonstrated their true potential. Neither employed massed attack, preferring to work singly or in small groups to capitalize on the advantages of agility, surprise and good planning. The Italians were particularly imaginative, evolving craft and tactics to assault an Austro-Hungarian fleet snug in well-defended harbours. The British had to contend with poorer weather conditions and soon learned the value of larger and stronger hulls. They also discovered the threat posed by aircraft and fire from ashore, suffering losses from both despite small size and manoeuvrability. Experience did not turn the British away from hard-chine designs; they accepted a drop in performance in heavy weather in exchange for the benefit of really high speed in calmer water.
After World War I the British totally lost interest in coastal craft, being occupied with deep-sea imperial matters. The Italians went on initially to be joint front runners with the Germans, who saw in the small-torpedo boat a means of constructing useful naval tonnage outside treaty restrictions. Beneath the lax gaze of the regulating authorities they built and evaluated numerous hulls under sporting-club colours and, over a decade, identified what were to be the major S-boat characteristics: displacement hull, wood on light alloy construction, stability reserves for 533-mm (21-in) torpedoes and, finally, the small marine diesel. This type of engine required careful development and, once perfected, remained peculiar to German practice, with foreign navies never producing a satisfactory competitor despite the fire risks associated with petrol engines, for which they treated effect rather than cause by introducing self-sealing tanks and improved fire-extinguishing systems.
The Italian lsotta-Fraschini was an excellent petrol engine, used widely abroad until 1940; it was probably its very availability that inhibited comparable development elsewhere. During World War I the Italians found the small planing hull adequate for their Adriatic operations. Translated into the open-sea war of 1940-3 it proved unsatisfactory and was dropped in favour of a German type of round-bilge form.
A considerable increase in efficiency resulted in the abandoning of direct-drive for purpose-designed reduction gearboxes and propellers, though transmission problems and structural failures proliferated with small hulls that ‘worked’ in a seaway. Wood had the necessary resilience and ease of repair where clad on timber or light alloy frames. All-aluminium alloy hulls corroded disastrous salt-water conditions. As in the pre-transitional navy, it was found that wooden hulls could not exceed a certain length and, for instance in the British SGBs steel had to be used. A great British innovation was to abandon traditional boat-building methods for mass production, using prefabricated techniques. Once certain weaknesses had been rectified, this system realized greater numbers of craft.
Hard-used fast coastal craft have a short operational life and demand continual attention. Specialized depot ships, or tenders, enabled squadrons to operate successfully ‘up-front’. The Americans particularly made great use of them, offering off duty crews accommodation and facilities while undertaking endless hull and machinery repairs, and servicing armament.
It had been assumed between the wars that coastal craft would be needed in inshore ASW role, a belief that hung on until the British SDBs of the 1950s. In the event, submarines generally operated further offshore and those which were destroyed by small craft were despatched by torpedo while navigating on the surface. Specialist AS boats were, therefore, rapidly re-armed as gunboats, their depth charges removed. It remained the practice, however, for many boats to retain a pair of charges for the deterrence of close pursuit.
Small torpedoes of up to 457-mm (18-in) calibre proved to have insufficient ship-stopping capacity, but the size and weight of two or four 533-mm (21-in) weapons tended to dictate the parameters of the boats themselves, to the extent that the Americans developed a special ‘short’ version. To save the weight of tubes, dropping gear was introduced, though this left the torpedoes themselves vulnerable to damage. The Germans preferred to retain their two enclosed tubes forward, with a reload for each stowed safely behind a bulwark.
Close-in fighting was typically brief and bloody, involving large volumes of volumes from light automatic weapons. Armour was gradually introduced as a result the Germans going as far as an armoured wheelhouse. Initially the British were at a disadvantage with only machine-guns to match the German 20-mm cannon, whose explosive or incendiary shells were lethal to wooden hulls loaded with petrol and ammunition.
As ever, armament developed to suit the need. American PT boats, involved in the Far East against the eternal and apparently unstoppable Japanese barge traffic, shed some or all of their torpedoes in favour of weapons such as racked 127-mm (5-in) rockets and 81-mm (3.2-in) mortars. British boats faced similar problems with the German MFPs, or ‘F’ lighters, in such areas as the Aegean and Adriatic. Like the Japanese, these craft were of a draught too shallow to be vulnerable torpedoes and could take aboard a variable armament which often included much-respected 88–mm (3.46-mm) gun. British MGBs responded appropriately, toting guns as large as the short-barrelled 114-mm (4.5-in) gun.
Radar, available to small craft, was a boon in the vicious nocturnal encounters where opponents could usually be seen only fleetingly and for very short periods. Paradoxically, it was radar-controlled gunfire on the part of larger ships that offset the torpedo boat’s advantages by effectively outranging its main weapon.
Come the peace there was no sentiment, the boats being deleted in hundreds destroyed by burning and many surviving a swords-to-ploughshares transfiguration to become houseboats of surprising durability.
Interest in small craft lapsed again on the part of the larger navies until that day in 1967 when the Eilat became the first major SSM casualty.