Deltic History
Napier Heritage

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Deltic History:  Napier Heritage

Having seen your web site I thought you might be interested in knowing the history that lies behind the company that made the Deltic engines that powered the Nasty boats.  As a consequence, I am attaching my version of the story of D. Napier & Son Ltd. Incidentally, my friend Yannis Colias, who now lives nearby in Portsmouth UK, was the commander of the Nasty boats when he was in the Greek Navy.  I am trying to persuade him to write about his experiences with these small ships.

Best Regards
Peter Webberley

Napier Heritage

50 Years of Design Excellence


The Piston Engines of

D. Napier and Sons


Peter Webberley     Portsmouth University

Heritage Studies

MA Maritime Studies





Britain’s heritage is very much a story of its industrial progress. This progress has been lead by the excellent design and mechanical engineering, which has produced the engineers, tools and other mechanisms necessary for the production of goods for export. D. Napier & Son is an under-rated company which has not only manufactured superb products bringing credit to this country, but has also been responsible for the training of engineers to carry its standards of excellence to be used by other industries. Over a hundred apprentices each year passed through the Napier training program. This is the story of the piston engines, which would have been worked on by all apprentices.

The Creation of D Napier & Son

David Napier and his son James established the company in 1848, the year of revolutions.  They showed a variety of products at the great exhibition of 1851.  These included a centrifuge for separating sugar from molasses; a patent 24-hour ship’s registering compass and three sizes of steam powered printing and perfecting machines. 

After the death of David in 1873, James patented many machines for weighing and trimming gold and silver coins for the Royal Mint.  The care and quality of workmanship that went into these machines is equal to any Hepplewhite or Wedgewood antique.  An example is to be seen in the British Museum.

Napier Motors

After the death of James in 1895, his son Montague took over the business and designed and built motors.  In 1902 a Napier car won the International Gordon Bennett Trophy. Napier led British road vehicle development and introduced the world’s first 6-cylinder car engine.  Napier cars were owned by the rich and famous all over the world.  Also Napiers were renowned for their army vehicles, ambulances and taxis.  They were especially famous for their race performances particularly at Brooklands.  Car production ended in 1925, when Montague Napier decided to concentrate the Company’s efforts on engines.

Napier Marine

In 1903 Napier won the first International Harmsworth Trophy competition with a 40-foot steel skimming motor boat named ‘Napier’, fitted with a four cylinder 75 bhp. Napier engine.  At Cowes it went on to win a 26-mile handicap for motor launches.  This was the start of Napier’s marine involvement.  In 1905, ‘Napier II’, with twin 72 bhp Napier engines, won the Harmsworth Cup Trophy and broke the World Mile Speed Record at 29.9 miles per hour.

napierlion.jpg (29369 bytes)

A NAPIER LION 1,375 bhp engine was used to power Hubert Scott-Paine’s Speedboat ‘Miss Britain III’  When it took the World Water Speed Record in 1933  with an average speed over three runs of 100.132 mph, a record which stood for over 50 years.This was carried out in Southampton Water,  the fastest leg was recorded as 102.105 mph  and this was against the tide.

Photograph and statistics by courtesy of Ensign Publications as they were taken from Adrian Rance’s book ‘Fast Boats and Flying Boats’.  


It was during the First World War that Napier entered the aero-engine field.  To start with, this was building engines to the design of the Royal Aircraft Factory at Farnborough and later designed by Sunbeam, but these engines proved so indifferent and troublesome that in 1916 Napiers decided that they could do better, and so designed their own broad arrow design engine that was to be called the Lion.  Unfortunately the engine was not installed into an aircraft until just after hostilities had ceased.

Napiers realized the fundamental features for an aero-engine, low weight, smallest possible frontal area and maximum power, this generally means squeezing many cylinders into a small volume.  This was achieved with the Lion by having three banks of four cylinders. This brought about the familiar, three bulges along the engine nacelle that became the unofficial ‘trade mark’ for the Lion engine.  Each cylinder had two inlet and two exhaust valves operated by double overhead camshafts for each of the three banks, which are in ‘broad arrowhead’ form.
napierendview.jpg (18774 bytes) Rear End View of the 12 Cylinder Napier Lion Engine 

The performance of this engine was greatly improved when in 1922 the engine was fitted with exhaust driven superchargers.  This was an early example of ‘turbo-charging’, which made the engine suitable for flying at high altitudes.  Napier Lion aircraft won the Schneider Trophy Seaplane races in 1922 and 1927.

The engine was later fitted in over 160 types of aircraft worldwide.  This must in itself be a record for popularity.


1919   Height Record of 30,500 feet.  
1929   Land Speed Record at 231.3 miles per hour.  
1929      Air Speed Record at 336.3 miles per hour.  
1930      Water Speed Record at 100.13 miles per hour. 1931   Land Speed Record at 246.1 miles per hour. 1932      Land Speed Record at 253.968 miles per hour. 1933      Air long Distance Record at 5,309 miles.  
1939      Land Speed Record at 369.74 miles per hour. 1947      Land Speed Record at 394.196 miles per hour.

NapierSupermarine2.jpg (13505 bytes)NapierSupermarine1.jpg (19561 bytes) Supermarine SE 5  Winner of 1927 Schneider Trophy Race.

This race lead to the design of some very beautiful seaplanes and eventually to the building of the famous Supermarine Spitfire fighter.

NapierGlostier.jpg (13632 bytes) Gloster IVA Biplane Achieved the Fastest Lap of 277 mph
 in the
1927 Schneider Trophy Race.


With the demand for more powerful and even more lightweight engines, in 1929 Napiers produced the 16-cylinder air cooled, supercharged ‘Rapier’ engines.  This was an overhead valve unit comprising two sets of vertically opposed banks of 4 cylinders driving twin crankshafts coupled to the single output gear on the centrally positioned propeller shaft, to make an ‘H’ form unit.  This arrangement produced 400bhp with a very small frontal area.  Being air-cooled reduced the weight of the engine and meant that a radiator was no longer needed, also reducing the overall weight.

NapierH.jpg (23693 bytes)

16 Cylinder ‘RAPIER’ Air Cooled Supercharged Aero-Engine.
The ‘H’ form of twin banks of vertically opposed cylinders may be clearly seen.  
This gave a slim, small frontal area to allow the pilot good visibility. 


NapierRapier.jpg (11372 bytes)

The Short Bros. Seaplane ‘Mercury’.
The efficient low weight and low drag ‘Rapier’ Engines enabled this aeroplane to capture yet another world record for Napier, the long distance record, 6,045 miles non-stop.  It was also the first and fastest aircraft to fly a commercial payload across the Atlantic Ocean.  World War II stopped further development 

The Dagger Engine

In 1933 the Rapier engine was followed by the somewhat similar Dagger engine.  This was also ‘H’ form and air-cooled but reverted to an overhead camshaft instead of push rods to operate the valves.  Also, the number of cylinders was increased to 24.  This engine could develop 1,000bhp.  The ‘Dagger’ incorporated such modern features as hydraulic control of rocker clearances and a variable pitch propeller.  Orders for these engines were slow initially, due to the lack of a re-armament programme by Britain.  After 1935, however, production was increased when ‘Dagger’ engines were fitted to the Handley Page ‘Hereford’ bombers and the Fairey ‘Battle’ fighter-bomber.  It was also used in the last biplane that the RAF ordered, the Army Co-operation and Ground Reconnaissance aeroplane, the Hawker Hector.

NapierRAF.jpg (15077 bytes) The last RAF biplane ordered for service.  The Hawker Hector fitted with an 800 bhp 24 cylinder ‘Dagger III’ engine. 


When World War II broke out it soon became clear that the Napier powered aircraft were too slow and the demand was for aircraft to be fitted with engines having in excess of 1,000 bhp.  Fortunately Rolls Royce had their Merlin engine in production for use by the Hawker Hurricane and the Supermarine Spitfire, but Napier’s answer, the ‘Sabre’ was not yet fully developed.

The Napier-Heston Racer, fitted with a ‘Sabre’ engine, had been built to achieve 485 miles per hour in answer to the Messerschmitt record of 469 miles per hour, but the outbreak of war caused the record attempt to be abandoned.
NapierHeston.jpg (10926 bytes)

Napier-Heston Racer built in 1939
Fitted with a ‘Sabre’ engine it was too late to complete 
its world speed record attempt before WW II broke out. 
A heavy landing in 1941 wrote it off

The ‘Sabre’ was also a 24-cylinder ‘H’ form engine but it was horizontally opposed, not vertical as were the Rapier and Dagger, and water-cooled, not air-cooled.  This engine had sleeve valves, and developed 2,200 bhp.  The radiator and oil cooler were carried in the air intake scoop below the engine, which gave the aircraft its distinctive ‘chin’.  It was a more powerful engine than its rival the Merlin and was fitted in the Hawker Typhoon, which was to replace the Hawker Hurricane.  The prototype Typhoon first flew in February 1940.

Although too late for the Battle of Britain, with its speed of 420miles per hour, this fighter was more than a match for the new Focke-Wulf 190, to give the RAF superiority in the air.  A new role was then found for the ‘Tiffy’ as the Typhoon was to become affectionately called.  This role was for the fighter to be used as a fast ground attack aircraft.  For this purpose it was fitted with four canons and eight rockets.  This gave it more firepower than a light cruiser.  It became famous for its ability to knock out enemy trains and tanks.

NapierHawker.jpg (14987 bytes) The HAWKER TYPHOON IB  in D-Day Markings  This aircraft is fitted with four cannons and eight rockets 

After the invasion it was found that there were problems with the engine, when the aeroplanes were operated from makeshift, dusty airfields.  This was through lack of suitable air filters, allowing the dust to cause wear in the cylinders.  Napiers reacted swiftly to the challenge.  Within a week they delivered, by air, a new momentum air filter, which fitted to the aircraft air intakes.  This permitted the Typhoons to be used to achieve the breakout through the Falaise Gap, which had held up the allied advance from Caen.

NapierTempist.jpg (12112 bytes) The HAWKER TEMPEST V Fighter Aircraft  

The Typhoon was superseded by the Hawker Tempest, which was faster and featured elliptical shaped wings reminiscent of the Spitfire.  Within the wings were fitted four cannons.  For this aircraft, the Sabre engine was fitted with a four bladed propeller and the power output had been increased to 2,600 bhp.  This made the fighter the fastest piston engined aircraft in the world with a speed of 460 mph, which was needed to catch the V1 ‘buzz-bombs’.  A development of the Tempest was the Hawker Fury which was fitted with the Sabre VII engine developing 3,000 bhp, with which it achieved a speed of 490 mph.
NapierFury.jpg (12138 bytes) Hawker Fury Fighter Aircraft

The Nomad Compound Engine

The basic fuel efficiency of engines is inherently in their design.  Some design features of different engines within a type may be altered to make one model marginally more efficient than another, but for practical purposes the fuel consumption of an engine depends upon its type and is of the order of the figures shown it the table below.



Ram Jet Engine

1.0 lb/hp/hr

Turbo-prop Jet Engine

0.8 lb/hp/hr

Petrol Engine

0.5 lb/hp/hr

Naturally Aspirated Diesel Engine

0.4 lb/hp/hr

Turbo-charged Diesel Engine

0.38 lb/hp/hr

Turbo-charged & Intercooled Diesel Engine

0.36 lb/hp/hr

Compound Engine

0.34 lb/hp/hr

The Nomad engine was a combined diesel and gas turbine engine.  It was designed to have the lowest fuel consumption of any aircraft engine by utilizing all the heat normally lost from the exhaust of the piston engine, to feed the gas turbine.  On the earlier model, the diesel drove one propeller and the gas turbine the other of a contra-rotating system.  Later a continuously variable gearbox was used to couple the two outputs together.  The engine was demonstrated in flight, at the Farnborough Air Show in 1956, fitted in the nose of a Lincoln Bomber.  The theory behind the design was for long distance flights, four tons of engine with one ton of fuel was a more economic proposition than one ton of engine and four tons of fuel.

The Nomad engine was designed at a time when simple ram jet engines were being used for high-speed fighter aircraft.  Lightweight turbo-prop jet engines driving propellers were replacing piston engines in existing airframes.  The Comet aircraft had not yet flown.

When the Comet first flew, it was discovered that the great savings in drag of the aircraft, brought about by high altitude flight, were greater than the losses through the inefficiency of the jet engine.  Propeller engine aircraft, which could not fly at high altitude, were overall less efficient regardless of the savings made by them having low fuel consumption.  This was the end of propeller driven commercial aircraft.  Development of the Nomad engine was, therefore, cancelled.


Many of our Motor Torpedo Boats and other high-speed craft were lost during the war because of the extremely inflammable fuel that they used.  The Germans employed diesel engines in their E-Boats, which were consequently less vulnerable.  The British Admiralty placed an order with Napier, for them to design and develop a diesel engine suitable for the post war high-speed craft.  The subsequent design was the Deltic engine.

Although complex in its layout, the Deltic engine is in fact fundamentally a very simple engine.  It is a two stroke, opposed piston engine, having the inlet ports in each cylinder, being opened and closed by one piston and the exhaust ports by the other.  There are neither cylinder heads nor poppet valves, and so no camshaft or other valve gear.  Being opposed piston means there must be two crankshafts for each cylinder bank; but by arranging the cylinders in an equilateral triangle means that only three crankshafts are required for the engine.  There are six cylinders to each bank and three banks to make the normal engine have 18 cylinders.  A variant having three banks of three cylinders was also built for generating electricity for magnetic mine sweeping.

NapierDeltic.jpg (29927 bytes) SECTION OF A DELTIC ENGINE

For the engine proper, the only moving parts are the pistons, connecting rods and crankshaft.  There is a fuel injection system with one pump per cylinder.  Being a two stroke, the engine needs a supercharger, which is a gear-driven centrifugal compressor.  As the engine is self-contained it also has the dry sump lubrication system and water cooling system.  The engine also incorporates a seawater circulating pump and an ahead and astern gearbox complete with hydraulic clutch.  The engine has aluminium castings for lightweight, with stainless steel studs and aluminum bronze nuts for high corrosion resistance.  This means that the engine has a very low magnetic weight, which makes the unit eminently suitable for mine sweeping duties.

NapierDark.jpg (17344 bytes) Dark Avenger’ one of the Royal Navy’s Short Boats

The original engine developed 2,500bhp at 2,000rpm and was used to power ‘Dark Avenger’ the first of 17 ‘Short Boats’ the ‘Dark’ class of MTBs built for the Royal Navy.  A lower rating of 1,500 bhp at 1,750 rpm was used for the Coastal Minesweepers.  The first of these was HMS Highburton, this class was originally powered, some with Mirrlees Blackstone engines and some with Deltics.  The Deltics proved to be so superior in service that the Mirrlees boats were re-engined with Deltics.  Later versions of the coastal minesweepers had their hulls constructed of GRP.

NapierHMS.jpg (9013 bytes) HMS HIGHBURTON the first Deltic Powered Coastal Minesweeper

The compact size of the engine is the reason for it being used for many different vessels.  One of the most successful was the Norwegian ‘Nasty’ class of MTBs.  In addition to Norway, the USA, Germany and Greece used these boats.  These were fitted with the more powerful turbo-charged version delivering 3,100 bhp and were capable of 45 knots.  A Japanese Navy fast patrol boat fitted with 3 Deltic CT18-42K engines delivering almost 3,700 bhp was capable of 50 knots. 

Both the nine cylinder and the eighteen cylinder engines were used for diesel-electric rail traction.  The former was in a type II locomotive and two eighteen cylinder sets were fitted in the famous ‘Deltic’ type V.  The prototype Deltic locomotive ‘Enterprise’ is currently on exhibition in the British Museum.  These were the only diesel locomotives cleared to run at 100 mph.

NapierV.jpg (15019 bytes) Type V ‘DELTIC’ Diesel-electric Main Line Locomotive 


Napier engines were always very different from others.  With the changing form of the engines from ‘W’ (broad arrow) ‘Lion’, to vertical ‘H’ ‘Rapier’ and ‘Dagger’,  to horizontal ‘H’ ‘Sabre’ and to the triangular ‘Deltic, they form a unique set not used by any other main engine builder.  However, in different ways they were each a world beater, squeezing more cylinders into a small volume to give a remarkable power to weight ratio and power to volume ratio.  It is doubtful if the power to weight ratio of less than 0.75 lb per bhp of the Sabre engine will ever be surpassed by another piston engine.  Nor will the less than 4 lb per bhp of the Deltic be beaten by another diesel.

No country in the world has moved ahead, the speed performance on land, sea and air by vehicles, as much as Britain.  Also, if the measure of progress is by the number of world records broken, then D. Napier & Son must rank as the geatest mechanical engineering company that ever existed. 

It is sad that in these modern times, companies need to be large in order to exist.  It was during the World War II that the Ministry of War Production brought about the absorption of Napiers into the giant English Electric Group of Companies, so that Napier lost a great deal of its individuality.  But it was even sadder when in the 1960s economic forces drove English Electric to sell off the aircraft engine departments to be lost within the rival Rolls Royce Company, and for the marine departments to be sold off, then to be lost within the great David Paxman & Company.  This small company with the great history is now being forgotten.


The author was employed by D Napier & Son. from 1947 until 1960, the first four years as a Student Apprentice and the last seven as a designer working on the Deltic.  During his time there he had the opportunity to work on the Sealion, Sabre, Nomad and Deltic engines.  He gratefully acknowledges the help and training he received and the assistance he obtained from his colleagues.

The photographs and much of the history of Napiers was taken from Alan Vessey’s grand book ‘Napier Powered’ printed by The Chalford Publishing Company Stroud.

He also wishes to acknowledge the help given by members of the ‘Napier Power Heritage Trust’ which is struggling to keep the fame of Napier engineering alive.

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