CMB9

This historic vessel was built as a motor torpedo boat for the Royal Navy in 1916 by Thornycroft, and named CMB 9 (Coastal Motor Boat 9).  She is of double diagonal mahogany construction and was one of twelve such vessels ordered by The Admiralty.  She was originally based at Osea Island on the River Blackwater in Essex and later served at Dunkirk.

The vessel saw action in 1917 off Zeebrugge during a dramatic mission accompanied by CMB1.  Both vessels were serving on the Dover patrol and went to the rescue of pilots who had been shot down ten miles off Nieuport. They came under attack by four German torpedo boats: CMB1 took a direct hit and was blown up, but CMB9 escaped unscathed. 

On 10 September 1917 a Top Secret memo was sent from the Admiralty to the DOD [Director of Operations Division] It stated: ‘I am to acquaint you that four of the existing 40ft [coastal motor] boats [CMBs] from Dover are to be used as Distant Control Boats [DCBs], and the First Sea Lord [Sir Rosslyn Wemyss] has stated: ‘I understand that the engines can be shifted aft. This question of employment should come under the DOD who is requested to take it up with the Third Sea Lord’. The Order was issued ‘By Command of their Lordships’.

So began a series of top secret experiments designed to test whether unmanned fast patrol boats armed with torpedoes could be controlled from the air and directed towards enemy targets.  One of the four boats selected was CMB9, which was re-designated DCB1. The vessel was to be controlled via aircraft and fitted with twin screws, bilge keels, radio masts and a small bridge with wireless controls, which would allow for the element of surprise whilst attacking the enemy.

The proposal was not universally supported. An Admiralty memo noted that ‘the only qualification which points to the CMB type of boat being used for this service is speed. Every other consideration shows the unsuitability of design, notably the necessity for all the weight being aft’.  It nevertheless conceded that approval had already been given at the highest level for the trials to take place. ‘It has been decided however to allot 4 40-ft boats for experimental purposes. They have the speed, and having seen considerable service, can better be expended, observing also that they cost £3,000 as compared to £7,000 for the 55-ft boats: moreover, the single engine is easier to control that a pair of such engines’.     

The writer’s concerns were soon proved well-founded. In his view ‘better results would be obtained by building a suitable type of boat designed to carry the necessary weight forward with the engines placed well aft, the exact reverse being the case with the present design of CMBs’.

One of the officers involved in the experiments, both towards the end of the war and immediately after it, was Lt Sidney Rayner RNVR. His job was to take the boat out into the Solent where he would link up with a plane flying overhead. The plane would take over control of the boat while he and his crew stood by in case anything went wrong.

On one occasion a number of senior Admiralty officials came down to Portsmouth to view the experiments. They were taken out into the Solent in a barge. The plan was that CMB9 would do several runs past them, controlled from the aeroplane. The bow of the boat was packed with material intended to represent the high explosive that would be placed inside the boat in an operational situation.

Lt Rayner was preparing to hand over control to the plane at the start of the first run past when water began pouring into the boat. The timber frames had opened up because of the weight of material placed inside. Faced with the possibility of the boat filling up with water and sinking Lt Reyner opened the throttle to raise the bow, and then made a beeline to Portsmouth Harbour, where the shore crew swiftly cradled her out of the water before she sank.

During 1918 satisfactory runs were carried out, with an aeroplane controlling the boat by wireless from a height of 16,000 feet and a distance of 5 miles.  Tests had shown that the height and distance from which the boat could be controlled were only limited by the visibility. The controlling gear, both transmitting and receiving, could, it was thought, be made to operate for a period of four hours within the year. Satisfactory runs had also been carried out by moonlight.   

Distant Control Boats were never used operationally during the First World War, but their development continued for me years afterwards. The Final Report of the Post-War Questions Committee, in 1920, noted that ‘the weapon [a Distant Control Boat] is in a different category from all others in that it is capable of control up to the moment of hitting, and this fact alone justifies close attention to development.’

The Report continued: ‘Although still in their infancy, we have had it in evidence that these weapons are already capable of being handled in numbers: two of them can be controlled by one aircraft, three of them have been manoeuvred close to one another simultaneously without mutual interference, and probably as many as eight can be handled in a group if the groups are not within about four miles of one another’.

The Report found other strengths for Distant Control Boats. ‘We have been informed further that it is difficult, if not impossible, for an enemy to interfere with the control by wireless jambing (sic), since each boat works on a different wavelength, and the discovery of the wave length is a delicate operation. When the elements of surprise and attack in numbers are added, the difficulty of defence by this means is increased’.

 But the Report was also clear about their shortcomings. ‘Present disadvantages are that it is a daylight weapon only; that it is interfered with by a heavy sea, although the boat can be completely closed in; that it strikes on the water line, although with a heavier charge than any hitherto used; that it must be transported to the scene of action and slipped by a vessel of considerable size; that an aeroplane must be flown off to control each pair of boats.

 The most likely solution to the problems appeared to them ‘to lie in its development into a shallow or surface-running torpedo of great size, which could be made to dive to a given depth at the end of its attack’.

 Progress on the success of the trials and on the development of Distant Control Boats was considered by the Naval Anti-Aircraft Gunnery Committee in 1921. The conclusion of the Committee’s report was that ‘the Distant Control Boat, in view of its possibilities, merits uninterrupted research both in the perfection of the weapon itself and in the preparation of counter measures. In its present state of development, however, we are of the opinion that it is not a great menace to the Capital Ship’.

 The Committee’s report noted that ‘there is, of course, a possibility of DCBs releasing torpedoes so as to obtain a hit under water, but this is still in the future’. The continuing development of torpedoes was to play an important part in naval warfare during the Second World War. But in 1921 the Naval Anti-Aircraft Gunnery Committee was able to note that ‘the control of DCBs by wireless has been definitely accomplished in our Navy’.

 By the outbreak of the Second World War the development of self-propelled weapons (torpedoes) had already reached the point where Distant Control Boats, as weapons that could be controlled from the air, were obsolete. They needed aeroplanes to guide them, and if they struck their target the boat itself was destroyed. They were however an important step in the development of unmanned weapons.

 It appears that DCB1 returned to her former role as a Coastal Motor Boat once the trails were completed. As CMB9 she remained in service with the Royal Navy until the early 1950s. It seems that she carried out the routine duties of a Coastal Motor Boat  during the Second World War.   

Where is she now?

DCB1 is currently undergoing restoration to full operation condition with the aim that she will return, by sea, to visit the old Navy bases where she was once stationed.

Sources

Formation of a committee to investigate the possible construction of coastal motor boats for experimental purposes. ADM1/8771/165. The National Archives.

Memo from Admiralty Board to Director of Operations Division (DOD) 10 September 1917, M.011240 (Secret). The National Archives.

Final Report of the Post-War Questions Committee, 27 March 1920, Distant Control Boat, CB.01557 (Secret). ADM 1/8586/70. The National Archives.

Wartime Recollections of Lt Sidney Rayner RNVR, reported by Tom Rayner 20 January 2015.