Hornets of the Sea

Early in WW1, three Royal Naval Air Service officers approached the Admiralty with the idea for a fast torpedo boat of shallow draught and, thus, capable of passing over German minefields and torpedo nets to attack the German Navy in their supposedly-safe anchorages.  The RNAS officers had developed the idea from John Thorneycroft’s hydroplane speedboats, capable of 35 knots and winners of several competitions prior to the war.  The Admiralty liked the idea and approached several boat builders, but only Thorneycroft’s was able to meet the requirement for a light-weight 40’ boat capable of being hoisted on the davits of a cruiser whilst armed with a single 18” torpedo.  To save on weight there was no conventional torpedo tube.  Instead, the torpedo was launched from the stern (the sting in the tail) and, once the propellors started, the coxswain of the boat had to make a sharp turn to avoid the torpedo’s path!  The new boats were christened Coastal Motor Boats (CMBs) and naturally, their existence was top secret.

The first 12 boats were delivered to the Admiralty in August 1916 and after trials in their use at night, the 3rd CMB division was despatched to Dunkirk in December.  In 1917, Lewis guns were added to the CMBs and they enjoyed success against a group of German destroyers off the coast of Zeebrugge.  Thereafter, they became the scourge of the German Navy and the Germans had hopes of capturing one in order to build their own versions.  In all, 39 of the 40’ CMBs were built, but so successful had the CMBs become, the Admiralty ordered a larger 55’ version capable of 40 knots and carrying two torpedoes, or one torpedo and four depth charges. 

A combination of 40’ and 55’ CMBs were deployed in the raid on Zeebrugge in 1918, acting as markers for the assault force, laying smoke or attacking German ships.  I give an account of the various actions of the CMBs in my novel The Suicide Club.

After WW1, the CMBs continued operations and were instrumental in the 1919 campaign against the Bolsheviks in the Baltic of which more anon in the final book of my For Those in Peril WW1 series. 

The 55’ (and a few 70’) CMBs continued service into WW2 and were the forerunners of the famous MTBs.  CMB 4, a 40’ version, is preserved in Portsmouth Historic Dockyard.  MTB 331, the last surviving 50’ CMB, is also, in Hampshire and CMB 103, a 70’ MTB, is on display in Chatham Historic Dockyard.

There seems to be little written about the history of the CMBs, but I was fortunate to find in the US an old copy of John Thorneycroft’s own history of the boats.