Coastal Motor Boats; Thornycroft and the Origins of Fast Attack Boats. By Martin Kelly and David Collins. Seaforth Publishing, Yorkshire, 2025.
Reviewed by Tim Coyle
The cover of Coastal Motor Boats depicts two Royal Navy 55-foot Coastal Motor Boats (CMB) in a night action off Flanders in 1918. The coast is illuminated by a searchlight and an explosion.
One CMB has slipped its torpedo and has turned hard to starboard through shore-based fire, raising waterspouts; its torpedo wake is barely visible headed for the explosion near the shore. The second CMB is seen from the port quarter headed for the torpedo release point, its torpedo nested in the trough aft of the steering position from which it will be loosed, followed by a sharp turn away.
The CMB story – ably told by the authors Kelly and Griffiths – is a ‘boutique’ history. Stemming from an experimental ‘cottage’ industry, founded by John Isaac Thornycroft in the late 19th century, the physics and engineering of the ‘skimming’, or ‘planing hull’ was developed for speed in association with the internal combustion engine. The book traces the type’s early development as a sport platform, moving to induction into the Royal Navy and deployment in the Dover-Zeebrugge area of the North Sea in 1917-1918. However, it was in 1919 that the CMBs came into their own through operations in support of the anti-Bolshevik White Russian armies in the Black and Caspian Seas and in Norh Russia. It was the spectacular sinking of the Bolshevik cruiser Oleg and the raid on the Kronstadt naval base that won plaudits for the CMBs and their daring crews led by Lieutenant Augustus Agar.
The book examines:
The Thornycroft company, its principals and their early experimentations to 1908;
Development of the Thornycroft ‘Miranda’ planing system 1908 to 1914;
The development of the CMB concept – the RN sponsors and supporters 1914 -1915;
The building of CMB 1;
Enry into operations August-December 1916;
New CMB designs, basing and logistics 1917 – 1918;
Experiments with ‘Distantly Controlled Boats’ (radio control) 1917-1918, and
Operations up to the Armistice thence transitioning to the Caspian Sea, North Russia and the Baltic 1918-1919.
Australian readers will be interested to note that one of the main instigators of the CMB concept, Lieutenant Geoffrey Hampden, was the Gunnery Officer in HMAS Sydney in the action with SMS Emden. He was the main signatory of a letter to the famously combative Harwich Force commander, Commodore Reginald Tyrwhitt, (reproduced in the book’s Appendix B) which advocated the use of fast attack craft in coastal operations. Tyrwhitt enthusiastically embraced the concept as did his close friend Commodore Roger Keyes who subsequently used CMBs in the Ostend and Zeebrugge raids.
The CMBs drew many to support and operate them who had a passion for unconventional naval warfare. Numbered among these was the enigmatic Erskine Childers – an expert pre-war yachtsman with incomparable knowledge of the North Sea and the Frisian Islands. He authored the novel Riddle of the Sands in1903 which propounded a scenario for a German invasion of Britain launched from the Frisians. The book is regarded by many as the first and best ‘spy’ novel. Childers was serving as a Royal Naval Volunteer Reserve Lieutenant and undertook many air reconnaissance missions using his local knowledge. He took an active role in planning the subsequently aborted Operation MB – a CMB attack on the German High Sea Fleet at its main anchorage in the Jade River.
Undoubtedly the demise of Operation MB was the biggest disappointment of the RN CMB era. This concept of a massed CMB attack against a fleet base was the purpose for which the CMB was designed. The book devotes Chapter Five to this operation, in which Childers is featured and describes the frustrations encountered which led to its cancellation. Although the CMBs were in action in the Ostend and Zeebrugge raids, and their capabilities were useful in routine coastal operations, they had to wait until 1919 – in the secret war against the Bolsheviks – to prove their mettle. The apogee of CMB raids was the attack on the Kronstadt naval base, commanded by Lieutenant Augustus Agar, for which he was awarded the Victoria Cross.
Apart from officers, the boats carried Motor Mechanics, rated as such for hostilities only. Mostly young, they were rapidly promoted to Chief Motor Mechanics. The CMB engines were fearsomely unreliable, with a propensity to ‘drop big ends’ which hindered their operations. The horrendous conditions the CMMs had to endure in effecting engine changes in the field are described in the book.
The initial chapters of Coastal Motor Boats profile the Thornycroft family engaged in early experimentation leading to the Miranda system using their testing tanks and instrumentation. The associated images show the bucolic nature of their environment – their residences and riverside activities in Edwardian England.
Postwar saw the reduction in CMB operations and Admiralty interest in fast attack craft waned. The CMBs were gradually paid off or used as targets with some transferred to foreign navies. Thornycroft sought foreign marketing opportunities and numbers of CMBs were sold to a variety of smaller navies – from the Baltic to China, Thailand and Japan – although a number of sales failed to complete.
The book documents all remaining traces of the CMB era. CMB 4 was preserved in an altered state. CMB 86 was found by a Russian underwater exploration group in 2022 near Hogland Island in the Baltic. CMB 86 was on the Kronstadt raid but failed to reach the target and sank under tow. The book shows a photogrammetric image of the boat sitting on the bottom in good condition.
In the final chapter of Coastal Motor Boats, the reader is treated to a description of the exciting recreation of CMB 4R. From 2017 to 2024 a team of enthusiasts, using the above-mentioned CMB 4 as a template, built an operational replica. All stages of the construction are supported by detailed images.
Maps of CMB areas of operation and the raids undertaken are provided and the Appendices cover ‘What Remains’ – boats and artifacts in collections and private hands, and ‘CMB Details, Histories and Dispositions’ – all the boats built or planned for military purposes.
Coastal Motor Boats will appeal to maritime historians, modellers and wooden boat enthusiasts. Technical aspects of design and construction, combined with the dramatic operational narrative attract the reader to this unconventional naval war with its disappointments and successes. Many extraordinary characters appear in the story and rank in the same exotic mould as World War One aviators.
So did the CMB story end when the RN withdrew from the Baltic in 1919? Decidedly not. Despite the interwar lacuna it took a new generation of visionaries – many of them volunteer reservists – to forge the RN Coastal Forces MTBs and MGBs of the Second World War. The US Navy developed the Elco PT Boats and the Axis also used ‘mosquito fleets’.
And in 2025 we are seeing small, unmanned attack craft undertaking CMB-type operations. Ukraine, ostensibly without a conventional navy, has used indigenous designs to cower the Russian Black Sea Fleet. Lieutenant Augustus Agar VC, and his CMB shipmates. would be proud.
