The Blockade Runners

During World War 2, from October 1943 to March 1944, the Gay Viking class of fast merchantmen ran the German blockade of the Skagerrak to bring vital ball bearings from Sweden to the UK. These converted Motor Gun Boats were powered by Paxman VEE RB engines. The following magazine article, published in the November 1979 issue of Marine Propulsion, tells the story.

The Blockade Runners

Fast diesel powered "coasters" ferried Britain's vital supplies during World War II

During a five month period from October 1943 to March 1944, one of the most amazing operations of the Second World War was undertaken. This entailed the running from the UK of merchant high speed launches into Sweden to bring back ball bearings, vital to Great Britain's war effort and only available from the former country. The story had not been told until recently because of the 30-year rule on security matters and even now parts of it are still classified. Apart from the almost swashbuckling aspects of the voyages themselves, the story encompasses the development of an advanced high-speed marine diesel in the UK and a class of Motor Gun Boats (MGBs), one of which later became the world's first vessel with gas turbine machinery.

To go back to the beginning, just before the Second World War broke out, the Turkish Navy ordered eight Motor Gun Boats (MGBs) from Camper and Nicholson, of Gosport and Northam, in the UK. Larger than the contemporary Royal Navy units built by Vospers and the British Power Boat Co., these vessels were also unusual in being specified for diesel propulsion, namely with three of the 16 cylinder Paxman VRB design units rated at 1000 bhp at 1750 rev/min, the history of which is described below. The original particulars of the class are given in the accompanying table.

Before completion of the class, the Second World War had broken out and they were taken over by the Royal Navy. Three of the class (see table) were completed as intended with an armament of guns and torpedoes though the last had to be fitted with Packard petrol engines as not enough Paxman VRBs were available. The other five, before completion, were assigned to "Operation Bridford". Bridford arose because the UK was dependent on Swedish ball bearings, from SKF, and also needed other specialist equipment to keep production plants running. These were being flown out of Sweden in small quantities but the need was for far greater supplies. At this stage, Sir George Binney, a buccaneering character who had already brought out to the UK a number of Norwegian vessels interned in Sweden in 1940, suggested the use of fast motor boats.

After some deliberation by the Admiralty and Foreign Office, the five Camper and Nicholson boats were assigned to the operation and drastically altered. The hull, forward and aft of the engine room, was gutted to form holds (total deadweight 45 tons) and a new merchant-vessel-like bridge structure constructed aft of amidships. This contained accommodation, galley, radio room etc., and was surmounted by a small open wheelhouse. A lightweight mast and derrick was rigged forward and some protective armament installed.

For political reasons, the vessels were run under the red ensign with Ellerman Wilson officers and Hull trawlermen providing many of the crew - all operations were run out of the Humber. As converted, the boats' speeds came down to a 23 knot maximum, with a maximum cruise of 20 knots and a range of 1200 miles at 17 knots.

"Operation Bridford"

All five blockade runners were completed in 1943 - three conversions being done by Camper and Nicholson and two by Amos and Smith, of Hull - but the operations did not commence until September 1943 when adequate hours of darkness were available. The plan required the boats to sail late in the afternoon, arriving early morning two days later in Sweden having passed through the Skagerrak during the previous evening's hours of darkness. This was the most dangerous part of the voyage with German naval forces constantly patrolling the area from their bases in Norway and Denmark.

The loading port in Sweden was Lysekil and it was hoped to sail on the evening of arrival and be back in the Humber two days later in the morning. In practice such a schedule was rarely achieved for a variety of problems arose.

The first run was scheduled to commence on September 23rd 1943 but was postponed one month because of engine bearing problems, and commenced with all five vessels sailing on the evening of October 26th. Only GAY VIKING reached Sweden, the others turning back because of bad weather and mechanical problems. By October 31st, GAY VIKING had returned with 40 tons of cargo, the normal load.

Gay Viking
Gay Viking

During the next five months, eight further successful round trips were completed, bringing the total cargo carried over the period to 347.5 tons against the planned for 400 tons. Over the same period of time, flights by aircraft carried 88 tons to the UK. The operations were not completed without loss, MASTER STANDFAST being captured by German forces on November 2nd, without ever completing a round trip, while NONSUCH only managed one round trip due to breaking two crankshafts (centre engine on December 24th and port engine on February 2nd).

HOPEWELL completed two trips but broke its centre engine crankshaft on March 6th, while the two "Gay" boats carried out three voyages but both also suffered crank problems - GAY CORSAIR damaging its centre unit on March 8th and GAY VIKING its port unit on March 17th. Reasons behind this crankshaft problem are detailed separately but it proved to be a major trouble spot during "Operation Bridford". Nevertheless, against all adversity, the objectives were met and most of the required cargo shipped. The blockade runners proved overall to be successful with their low silhouette and relatively high speeds (certainly amongst the fastest merchant coasters ever built) and if Paxmans had had more time to test and develop their VRB engines, in excess of 400 tons could have been shipped.

Evolution of an engine family

Seven of the eight Camper and Nicholson gunboats were powered by Paxman high speed marine diesels. This engine was very advanced for its time and has a most unusual evolution, as we learnt recently when talking to A G Howe, Technical Director of Davey Paxman from 1936 to 1966.

The original concept was suggested to "Ted" Paxman by General A E Davidson of the Royal Arsenal, Woolwich. At that time, the late thirties, war was looming up and General Davidson proposed the development of a diesel engine of about 600 bhp which would be suitable for the propulsion of large tanks. Paxmans set to work and firstly adopted a vee-form despite the dislike for this configuration by orthodox engineers (difficult to maintain etc.). The original design had the crankshaft supported in the bedplate, the conventional arrangement for the 1930s. This was soon changed to a then more un-conventional system with the bearings underslung to improve rigidity and reduce weight. The prototype, a 12-cylinder unit, was in practice installed in the Army and Navy Stores power station in London in 1938. This engine suffered a crankshaft failure some two years later (presaging one of the few problems with the design) and was replaced at the end of the war by a Paxman RPH which we understand is still operational today as a standby unit.

Despite not being used initially as a military unit, the Paxman design found favour with a number of users in roles such as mobile generators and pumping sets. Maintenance was found to be relatively easy - for example pistons could be withdrawn through the crankcase doors. The engine design itself was of a 60° vee with 7 in bore and 7¾ in stroke. Exhausts were on the outside of the engine, and a Ricardo Comet combustion system was incorporated. Normal aspiration was used and at 1500 rev/min, a bmep of 88.5 lb/in2 achieved, together with a peak pressure of about 1200 lb/in2. The maximum output rating of the design as finally evolved was 62.5 bhp/cylinder at 1650 rev/min, not a high figure by today's standards but a considerable advance on the performance of the time.

First marine application

The first marine application of this design, known as the VRB, was on an experimental motor torpedo boat (MTB) called the "TARRET". This vessel, designed by F Gordon Pratt, of Cox and King, was built for the Royal Navy by Swan Hunter and Wigham Richardsons, of Wallsend, in 1939 and was powered by two 16 VRBs, each rated at 1000 bhp. A 110 ft long vessel of all-welded steel construction, it displaced 115 tons and achieved 30 knots on trials but without armament. The hull form was a successful attempt at achieving rough weather ability - it was a semi-planing design with concave sections turning to convex at the outer chine, the latter also being carried far higher forward than was then normal. The VRBs installed were of an early type with uncooled exhaust manifolds which glowed red hot during full power trials making attention to the combustion side, in the vee, highly dangerous! Despite its success, the "TARRET" was then considered to be too slow (though nowadays 30 knots is an acceptable maximum for fast patrol boats), and lightweight diesels of suitable power-to-weight ratio could not be produced in time for general adoption in fast fighting small craft.

In the meantime, other applications were being developed. One concerned tanks, the original inspiration of the engine. This was the T.O.G. ("The Old Gang") series, so called because the design team comprised the same people who produced the earliest British tanks during the First World War. Six were built (incorrect - only two TOG tanks were built. See Paxman's Tank Propellant page for details), each with a 600 bhp Paxman engine, but they did not prove a success. Equally unsuccessful was a plan to produce giant excavators for a proposed supply trench running forward from the Maginot Line. Each excavator was to have four engines (incorrect - only two engines in each - see Nellie section on Britannia Works page) and prototypes were built and tested, but the fall of France in 1940 led to cancellation of the plan. Nevertheless, Paxmans had received orders for 300 to 400 engines and these were later built and adapted to be fitted in tank landing craft. Some 5000 (incorrect - 3,533) of this design were finally constructed, these being the so-called three-part engine (TP). This was a modification of the construction technique to ease mass production. The crankcase was separated from the two cylinder blocks to produce three separate structures for simpler boring. Components were mass produced at numerous factories around the UK and then supplied to Paxman's factory at Colchester. Here they were assembled in about 60 hours by a woman and a boy.

Before these developments had come to fruition however, the VRB had achieved another marine contract. Following the partial success of the "TARRET" experiment, and with British Admiralty blessing, the engine was selected to power the eight Camper and Nicholson MGBs ordered by Turkey in 1940 and based on the RN's MGB501 of 1939. In the event only seven boats were Paxman-powered, each with three 16VRBs. Because of lack of supplies, the eighth had triple Packard petrol engines.

Problems in service

The VRBs fitted in the gunboats, five of which operated as merchant blockade runners, were similar to those in "TARRET" other than they had water cooled exhaust manifolds, manufactured in cupro-nickel. There were water cooled silencers too which both considerably quietened the engines and eliminated smoky exhausts. Due to wartime pressures, the engines were given the minimum of testing (normal Admiralty specifications would have required a 2000 hour continuous test). Unfortunately this led to some detail design faults showing up in service rather than on the testbed. The initial problems concerned big end bearings with white metal being found in the lub. oil but this was soon overcome. Also the tappets had wiper pads fitted, rather than rollers, and these wore badly on the cams themselves. Later they were redesigned to take rollers.

The major problem area concerned the crankshaft and in retrospect this is not surprising. At that time the majority of diesel engines of similar power output ran at speeds no higher than 750 rev/min, therefore 1650 rev/min represented a real advance into unknown territory. Four failures and one fracture occurred on the blockade runners over a three month period. The cause was torsional oscillation coupled with too small a section in way of the web and crank pin. The latter was hollow, concentrically to keep the torsional frequency as high as possible.

However, it weakened the section creating too high a stress concentration. The solution adopted was to offset the bored out section and increase the strength. Mr. A. G. Howe feels that the broken crankshafts were accentuated by the high constant speed running inherent in the blockade running operation. That the lessons were well learned is shown by the freedom from crankshaft problems in the descendants of the VRB. The family of high speed diesel engines stemming from the VRB led to the TP, described above and then to the RPH and the YH. This latter engine design formed the basis of knowledge and experience culminating in the current Ventura and Valenta range, thus completing evolution over 40 years and proving the soundness of the original VRB conception.


Length, o.a.117 ft 0 in.
Beam20 ft 3 in.
Draught, mean4 ft 1 in.
Displacement95 tons
Propulsion*3 x Paxman VRB engines
Total output*3000 bhp
Speed*28 knots (max)
 25 knots (continuous)
Endurance2000 miles at 11 knots
*MGB 509 was powered by three Packard supercharged petrol engines giving a total output of 4050 bhp and speeds of 31 knots (max), 27 knots (continuous).


502completed as MGB, became MGB 2002 in 1945, mined in Skagerrak 12/5/45.
503completed as MGB, became MGB 2003 in 1945.
504completed as HOPEWELL, became MGB 504 in 1944 and MGB 2004 in 1945.
505completed as NONSUCH, became MGB 505 in 1944 and MGB 2005 in 1945.
506completed as GAY VIKING, lost 5/2/45 returning from Sweden to UK, operation "Moonshine". Later raised and refitted. Known to have been in existence in 1970 as a pleasure craft in Bahamas as BAHAMAS VIKING.
507completed as GAY CORSAIR, became MGB 507 in 1944, and MGB 2007 in 1945. Stranded and foundered off Aberdeen 24/5/45.
508completed as MASTER STANDFAST, captured by German forces on 2/11/43 during "Operation Bridford".
509completed as MGB 509, became MGB 2009 in 1945. Converted to gas turbine propulsion (centre shaft) in 1947.

Subsequent History

Operations were ceased when the nights became shorter, but a second project, "Operation Moonshine", was run between September 1944 and February 1945. This operation entailed transferring weapons and demolition material to Sweden for onward movement to the Danish resistance. The exercise proved disastrous with a total of 20 trips attempted up to January 1945 unsuccessful due to bad weather in the North Sea, fog in the Humber, etc. HOPEWELL, NONSUCH and GAY VIKING were used on this run and the latter, on February 5th, 1945, was in collision on the return trip with the HOPEWELL. She was abandoned and sank though later was refloated.

Latterly, the survivors were reconverted and armed, and commissioned as MGBs. Of the eight boats in the class, only four survived after the war, and one of these MGB 509, latterly MGB 2009, was converted in 1947 for gas turbine propulsion on the centre shaft, but that is another story.

Note: The above article, as originally printed, referred to 'Operation Bridport'. SOE records released in 2002 show that this should be 'Bridford'. The text on this page has been amended accordingly.

An article about the Gay Viking Class was also pubished in The Marine Engineer, November and December 1944, entitled 'The "Gay Viking" Class Triple-screw Motorships'.

Page updated: 30 SEP 2008