In 1932 when the Air Ministry decided that they required a high speed mobile target for bombing practice, they approached Hubert Scott-Paine of the British Power Boat Company through their Marine Department with a view to providing a moving target with a speed of from 20 - 30 knots. A foursome comprising Scott-Paine Beaufort-Greenwood, T.E. Shaw and Captain Nicholson from Hadfields armour plating company, jointly evolved the Armoured Target Boat (ATB) for Aircrew Training. Working in conjunction with the Air Ministry they overcame several technical problems of the time. The ATB had to be constructed to keep at sea in all kinds of weather conditions at high speed and at the same time to have been capable of carrying an enormous load of armour and fuel. The machinery, petrol and personnel had to protected against direct hits from the bombing aircraft, and the ATB had to be rendered unsinkable. The space available dictated the installation of engine power which at the time was thought to be incpapble of efficient workng. Wireless had to be fitted, together with smoke screen devices and sufficient petrol fuel to enable the ATB to get to the bombing area and remain there for considerable periods of time.
One of the outstanding features of the ATB was the idea of housing the armour on rubber-fitted footings, which increased the efficiency of the armour considerably. A new material of hard expanded rubber which was considerably lighter than cork provided the necessary buoyancy in case the craft had a direct hit, and the arrangement of the triple screw machinery was carried out in such a manner as to disprove practically all the then known theories on the subject. The bombs dropped on the ATBs were 8lb or 11lb practice bombs. The crew, whilst on trials with the MAEE reported that they felt no ill effects from concussion when a bomb fell directly on the armoured plating. The 37.5ft ATB was an adaption of the well proven 37.5ft Seaplane Tender hull, but with a lower freeboard to reduce the excessive top-hamper, and the inclusion of a third engine to counteract the additional weight of the plating.
Two prototypes were built, RAF A190 and RAF A191 and were delivered within eight weeks from the time of formulating the concept. The first boat was on trials within six weeks from the date the order was received (May 1932). Initial trials on the Solent were successful, as the ATB attained just over 30 knots, however without armour fitted. Troughs were then erected where it was prposed to fit the armour, into which ballast was loaded, so as to represent working conditions with armour as nearly as possible. Trials were then carried out under those conditions and speeds of over 23 knots were obtained. Instructions were then issued to Hadfields Ltd to complete the armour for protection of the crew and machinery, fore and aft bulkheads and the sides of the craft in way of the crew, machinery and fuel. When the armour arrived it was fitted under the direction of Scott-Paine, so as to afford easy removal (or ease of access to machinery) and official trials were carried out.
Certain modifications were found to be necessary and thus in August 1932 the two craft were taken to Bridlington in order that actual operations with practice bombs could be carried out. However the armour was not shipped in position for the passage but arrangements had been made to despatch it direct to Bridlington for fitting on arrival. A canvas was fitted over the engines to form a cover to keep out salt water, however due to rough weather en route, the engines were subjected to salt water and one boat was reduced to one engine whilst the other lost all three engines. With one engine operating, one ATB towed the second out of breaking surf and prevented it from being damaged on the sandy beach off the Lincolnshire coast. The two craft made the safety of Grimsby where several days were spent repairing the craft. Further repairs were made at Bridlington on arrival and subsequently the armour was fitted. Eventually trials with bombs were carried out and proved successful. This resulted in an order for five more 37.5ft ATBs in 1933.
All the 37.5ft ATBs were later re-numbered with 500 being added to their original numbers - thus A190 became A590. The numbers of this type were limited by the fact that advancements in the aircraft of the time progressed at such a pace that larger bombs were required to be dropped and consequently additional protection was carrird. Further orders were for the larger 40ft ATBs.
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