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The RYPA (Roll, Yaw, Pitch, Alteration of Course Instructional Platform) was a British instruction and practice platform that could support Rangefinder and various Gunnery Director equipment. Similar to a cockpit simulator, it could rotate the equipment placed on it about various rotational axes to simulate the motion of a ship under way. RYPA equipment could be installed aboard a ship, but was perhaps more commonly fitted at shore installations.

Mark I Model

The Mark I model seems to have appeared around 1917 and was originally dubbed the Director Firing Teacher in the Director Firing Handbook,[1] as it hosted a British Tripod Director Firing System and taught its crew to shoot effectively while on a ship in a seaway. By 1920, it had been renamed RYPA Mark I.[2]

It had 1 H.P. electric motors running at 1,000 R.P.M. The Yaw Frame was supported on the roller path by three rollers. The yaw motor sat on its "port" side, and the "starboard" side had a semi-circular training rack across which the "alter course" motor could drive it. The Main Frame sat atop the Yaw Frame and carried the rolling and "kicking" mechanisms at its "fore" end, an electrical started and control panel at the "after" end, and two trunnion arms in which the director sight mounting was secured. Despite the "RYPA" name eventually adopted, the Mark I did not have a rotational axis corresponding to the pitching of own ship.

Irregularly shaped circular cams in the Yaw and Roll mechanisms introduced chaotic motions about the zero of each axis of rotation to mimic the rolling and yawing about its mean course of the firing vessel. Rolling to a maximum amplitude of 2.5, 5 and 7.5° were obtainable by shipping one of three roll cams, and yaws of 2 and 3° were likewise possible.

When the Director Layer's trigger was depressed, an air rifle affixed to the director's sighting arms and parallel to the telescopes would firem the projectile flying out to model ship targets in a catcher box and frame, and the kicker mechanism would cause the Main Frame to roll as if the power of a broadside had just been thrown, the magnitude of the kick being a function of the relative angle of fire so that fire on the beam produced the greatest kick. A time-limiting mechanism prevented "kicking" from occurring more often than a broadside might be fired and assured that the kick was instantaneous even if the trigger were held down.

The "alter course" function was operable by a controlling instructor and permitted deviations of up to 90 degrees either side of a nominal mean course for the exercise. In 1917, at least, alterations in course occurred at either 40 or 80° per minute.[3] The instructors also had a keyboard to control the RYPA:

  • Rolling motor start/stop switches
  • Yaw motor start/stop switches
  • Gun Ready Lamp pushes (pressing caused indicated lamp in the director to light, firing caused all lamps to go out)
  • Interrupter switches for Gun Ready Lamps and for Kicker (the latter breaks the firing circuit)
  • Target lamp switches to cause lamps behind each target ship to burn, to mimic firing on a ship only intermittently visible
  • Master emergency switch to cut off all motor functions
  • Target alter course switch, to cause model targets to yaw left and right

A variation of the Mark I RYPA permitted a British Lightweight Director Firing System to be fitted in lieu of the original tripod director sight.

Safety Measures

There were no explicit safety assurances that the airgun's bullet would be caught by the catcher box. Installations at shore establishments were encouraged to fit stops and post flags indicating where it was safe to walk where prudent and to have a bullet-proof background. Officers overseeing installation and use by ships at sea were to employ measures similar to those governing use of aiming rifles.

Mark II Model

The Mark II RYPA design introduced the Pitch axis that was absent in the Mark I design. Despite this improvement, it was substantially more compact than the earlier design owing to the use of a single motor for Roll, Yaw and Pitch motions.[4]

A Base Plate with a semi-circular rack hosted the equipment. The Main Frame sat atop it and had the "alter course" motor and mechanisms at the "port" side and the kicker gear, Roll, Yaw and Pitch motor and cams on the "starboard" side.

The reduced complexity of the engines meant a simpler keyboard for the instructor:

  • Pushes to start/stop Roll/Pitch/Yaw motor
  • Switches for Alter Course function:
    • Port turn (slow speed)
    • Starboard turn (slow speed)
    • Full speed
    • Stop
  • Kicker switch to simulate a salvo (presumably, when not wired through Director Layer's pistol)

See Also


  1. The Director Firing Handbook. pp. 139-140, Plate 83.
  2. Manual of Gunnery (Volume III) for His Majesty's Fleet, 1920. pp. 59-61.
  3. The Director Firing Handbook. p. 139.
  4. Manual of Gunnery (Volume III) for His Majesty's Fleet, 1920. pp. 61-62, Plates 93, 94.