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In the beginning of 1946, D. Napier  Son received a contract from the Admiralty to design, develop and manufacture :-

              (a)     Single Cylinder Unit (One leg of the Deltic)

              (b)     3 Cylinder Unit (One slice of the Deltic)

              (c)      6 x full size 18-Cylinder prototype / development engines


George Murray designed a Single Cylinder Unit between October and December 1946 followed by the 3-Cylinder Unit between January and May 1947.  The Single Cylinder unit ran successfully from January 1947 onwards.


The 3-Cylinder test unit ran spasmodically from October 1947 onwards, with a great deal of trouble due to out of balance forces and couplings.  The firing in the Crankshaft degrees was as follows:

            "  * 40 degree     * 40 degrees     * 270 degrees     * 40 degrees     * 40 degrees     * 270 degrees,  etc  "


This unit was abandoned but it did prove the design of the fork and blade connecting rod assembly.  In the meantime, the Scavenger Blower was designed, manufactured and rig tested from November 1947 onwards.  The main engine design also proceeded and was completed by the end of 1948.  Around this time a Compounded 18-cylinder version was considered and Single Unit Tests were run.


The first Engine D18/1 ran on the test bed in April 1950, constructed as what became the Deltic 18-11B producing 2,500 BHP at 2,000 RPM and intended for the motor torpedo boats the engines were designed for.


The Minesweeper version of the engine was designed and also the 9-Cylinder Pulse Generator Set.  Two of the six development engines built at Napier's Acton Works were installed in an ex-German E-boat (RN Pennant P5212) at HMS Hornet and ran extensive sea trials from late 1951 onwards, proving the Deltic as a successful design.


The Deltic engine design was fit for purpose and is still in use today fitted in the Royal Navy's Hunt Class Mine Counter Measures Vessels.  Whilst these boats are currently going through a modification process which includes the fitting of Caterpillar engines, it is incredible to think that 2016 will see 70 years since design of the engine commenced.


The sound (and feel) of Deltic engines can still be experienced today as six British Railways Type V 'Deltic' locomotives are preserves.  Furthermore a 9-cylinder Baby Detlic is being recreated.  In the USA there is a long term project to restore a US Navy Nasty Class MTB - PT3.

Two Stroke High Speed Diesel

Design E130  1946

18-cylinder 5.1/8" bore x 7.1/4" stroke

Three cylinders per bank arranged as an equilateral triangle.

9-cylinder version also constructed

Deltic 18-1 Prototype engine
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Deltic 18-12A Rail Engine as fitted in DP1
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Prototype of 3100 bhp Turbo charged T18-37K
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Where to see:

    Deltic Prototype (DP1), National Railway Museum, Shildon     Deltic 18-12A (2)

    Surviving Class 55 Locomotives (6)                                     2 x Deltic 18-25B engines each

    Baby Deltic Project, Barrow Hill Roundhouse, Nr. Chesterfield Deltic T9-29

    Deltic Preservation Society Depot, Barrow Hill Roundhouse, Nr, Chesterfield

                                                            Deltic 18-7A (2), 18-25B (11), T18-37K (1) and CT18-42K (1)

    Anson Engine Museum, Poynton                                Cutaway Deltic 18-25B


In 1943 the Admiralty convened a committee under the Chairmanship of Sir Roy Fedden to advise them on the future diesel engine for Fast Patrol Boats.  The 1939 - 45 war having proved the vulnerability of petrol engined boats.


The findings of the Committee recommended a 2-stroke Sleeve Valved Engine similar to the Napier Sabre in configuration.  A variety of companies were approached to tender for the design and manufacture of the engine.


The English Electric Company offered an alternative proposal which was to become the "Deltic" having had various technical arguments against the Fedden proposition.  In the E.E.Co. offer, it statated precisely that D. Napier & Son would undertake the design, development and manufacture.


Napier's unique solution was derived from the Napier Culverin aero-engine from of 10 years earlier, and design of the E130 Deltic commenced in 1946.  The engine is a two-stroke opposed piston compression ignition (diesel) engine having three or six banks of three cylinders in a triangular arrangement.  At each corner of this equilateral triangle is situated a crankshaft, each crank having an exhaust (fork) and inlet (blade) connecting rod from the two adjacent cylinders.