Chapter four


4.1. THE TYPE 159

4.2. THE TYPE 12

4.3. THE TYPE 45 AND TM 46


4.1. THE TYPE 159

In 1949 - S.R. Tanner`s team, occupying the top floor of the DECCA RECORD Co. building in Southwark Bridge Road, Kennington, was designing an experimental model of an X-band marine radar that was to become the TYPE 159.

The scanner comprised a pair of 4ft., horn fed, ‘cheese’ aerials mounted directly on top of a transmitter/receiver (modulator) box, which in turn was fixed to the turning gear. The upper horn and cheese reflector combination acted as the radiating element whilst the lower combination received the returned signals. The antenna design for the experimental model, with its combined scanner and RF head, employed a manual means of rotation, using a Bowden cable. Video signals were displayed on an A-scope.

The experimental Type159A was taken for preliminary trials to sea on the ‘MV Navigator’ (an ex Royal Navy ‘Fairmile’ vessel owned by the Company). The trials, conducted by a team led by M. H. Easy, were sufficiently encouraging to allow the next stage of production to proceed. The combined Antenna and RF Head of the production version Type 159B was then driven by an electric motor to rotate continuously at 20rpm. Video signals were displayed on a 9inch, rotating coil PPI display (Plan Position Indicator).

Four pre-production models of the Type 159B were made and satisfactorily tested on sea trials enabling the Type159 to be launched onto the worldwide market in 1950. It was competitively priced at £1500, whereas other British marine radars were on sale at over £3000 per installation. The Type 159B was an immediate success. A very large number were sold worldwide and established the platform on which rapid expansion of the Decca Radar Company would take place. (It has been said that the first Decca Radar was designated TYPE 159, because that was the number of the local London Transport bus that passed the door of the Decca building in Southwark Bridge Road).

Photo of Type 159B Display with 9 inch CRT Photo of Type 159B Horn Fed Double Cheese Antenna

4.2. THE TYPE 12

The second radar developed by DECCA was designated the Type 12 and was a higher specification version of the 159. It was supplied with a 12 inch CRT/Display and incorporated a Deccaplot (reflection plotter), which enabled marks to be made on the plotting surface to appear as though they were on the face of the CRT, (an early form of tracking).

4.3. THE TYPE 45 AND TM 46

Photo of Type 45

In 1952, the company commenced delivery of the Type 45, (to be known in the Royal Navy as the Type 974). It was similar to the Type 12 but with a six-foot horn fed aerial in place of the original four-foot design. This product was then followed, in 1955, with a ‘True Motion’ variant - the Type TM46. Ships heading and speed through the water were processed so that land echoes appeared stationary and the course of other shipping displayed correctly. Further developments led to a series of improved commercial marine radars and by 1958 Decca Radar had sold 7000 marine radars. In 1979, Decca Radars’ Marine Radar activities were acquired by Racal and the new Company went under the name of Decca-Racal. At the time of the Racal take-over it was said that Decca Radar had fitted marine radars to 50% of the worlds shipping.

The Decca TM46 was the worlds first ‘True Motion’ display. In the mid 1970’s Decca/Racal introduced the Bridgemaster series of Marine Radars. In December 1996 the U.S. Corporation Litton Industries bought out Decca/Racal Marine and in the year 2000 Northrop Grumman acquired Litton Industries.

Special Note: At the time of compiling this book it is known that the Northrop-Grunman Group of America continue to market Marine Radars under the Decca Banner. While our focus is mainly on the development of ‘Heavy’ ground and sea going radars, reference is made to the common roots of the respective Companies before their initial splitting in the 1960’s.


When Decca Radar’s Managing Director, Gp Capt. Fennessy persuaded the Plessey Company to buy the Heavy Radar Division of Decca, part of the agreement specified that Plessey would not compete with Decca in the Marine Field for several years. In 1966 the concept of a ‘Small Boat’ radar product was put before the Plessey Board of Directors and it was agreed that a team of design engineers would be established to develop the proposal. This radar was to become the MR 12 and be aimed at the high volume American (US) Leisure Market.

The radar was to be produced for ‘easy fit’, comprising just two units linked by only a cable harness.

The display unit was based on a rectangular (TV style) CRT, giving a 40% greater viewing area than an equivalent circular CRT. It was also, with all its support circuitry, contained in a volume of less than one cubic foot.

The masthead equipment was housed in a Radome, which reduced antenna rotation power consumption, allowing a lighter gauge of structural engineering, also providing protection against operating hazards such as rope entanglement.

All possible variations of primary boat power supply were accommodated, be they 12V or 24V DC, 115V or 240V at 50 or 60 Hz. A 400Hz alternator formed part of the system whilst the variant antenna drive motor was to be selected on purchase.

By using micro-logic techniques the system could be contained in just two units, providing both navigational and surveillance facilities with a range from 16 nautical miles down to 25 yards.

Features would include ‘easy to read’ electronically maintained heading and bearing alignments, sensor controlled picture brightness and reduced sea clutter with minimal adjustment after range scale changes. In engineering and ‘end user’ terms the product was an undoubted success but the long term profit from it was not to be gained by the Plessey Company. After a thorough development programme of ‘A’, ‘B’ and ‘P’ models, and the meeting of American RFI (Radio Frequency Interference) and FCCS (Federal Communications Commission standards), a successful product run for the MR 12 was established at Cowes on the Isle of Wight. The Plessey management subsequently took the view that the Isle of Wight was not the place for a ‘mass production’ run, so the product base was moved from Cowes to West Leigh. It was this delay that gave a Japanese based company the opportunity to come into the market with an almost identical product. It was the US Agent, BENMAR, based in Fort Lauderdale, Florida, that finally made the product into a success, the original contract with Plessey having been for some 6,000 units.

Photo of The two units of the MR12 Photo of MR12 Antenna Unit with Radome removed Photo of An exploded view of the MR12 Display Unit
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