CMB 4 - Coastal Motor Boat

The original batch of Coastal Motor Boats (CMB’s) were designed and constructed in 1916 by John I Thornycroft, and built at Platt’s Eyot at Richmond on the River Thames.  The War Department’s specification was for a fast, shallow-draught boat, capable of passing through a minefield and then delivering a single 18-inch Whitehead torpedo. “Coastal Motor Boat” was a “camouflage” term for the boat, so as to not give away its true purpose.

CMB 4 took part in raids on Zeebrugge and Oostende but, most famously, in two raids on the Bolshevik fleet in the port of Kronstadt in June and August 1919.  In the first daring raid, the cruiser “Oleg” was sunk outside Kronstadt Harbour, for which her commanding officer, Lieutenant Augustus Agar, was awarded the Victoria Cross and promoted to Lieutenant Commander. Seven CMBs took part in the second raid for which two other officers were awarded VCs and Agar was awarded the Distinguished Service Order.

A replica CMB is currently under construction in Boathouse 4.

CMB 4 is on loan from the Imperial War Museum.

Boat Stats

Length Overall



8ft 6in




4 tons


Originally Thornycroft RY12 V12 petrol engine 250 bhp.


Double skin mahogany

Date Built


Boat Yard

Platt's Eyot, Hampton, Richmond


Supported by:

Supported by Regional Growth Fund