A 17".7 torpedo powered by an eight cylinder radial steam engine and designed for use by aircraft and PT boats. Owing to its length, the Type 91 must be dropped from re-latively low heights; otherwise the head or tail would probably break off. Three different types of the torpedo and several types of warheads have been recovered. Because they vary widely in design and operation each type will be discussed separately on the following pages.

"TYPE 91, MODIFICATION 1"

Earliest of the Type 91 torpedos recovered, this model can be recognized by rivets on warhead, afterbody and tail. It is a single speed torpedo and leaves a partly visible wake.

The physical characteristics of the torpedo are as follows:

Length Overall – 17'3".

Length of Warhead – 3'1".

Length of Airflask – 8'11".5.

Length of Afterbody – 5'2".5 (Including Tail).

Diameter – 17".7.

Total Weight – 1730 lbs.

Charge – 338 lbs. Shimose, Type 94 or 97 explosive.

Tail Fins – 4, long horizontal, short vertical.

Range/Speed – 3300 yards at 42 knots.

Depth Setting – 6'6 to 52'8.

Warhead – Type 91, Modification 1.

Exploder – Type 90, Model 2, bail, impact-inertia in pocket on top centerline of war-head.

Operation

As the torpedo travels through the water, pressure depresses the bail on the explo-der. This unlocks an inertia trigger and frees the impeller. Rotation of the impeller arms the exploder, and impact with the target displaces the inertia trigger. This release the firing pin which, driven downward under spring pressure, strikes the detonator, firing the charge.

Safety Precautions

This torpedo must be considered dangerous if found in shallow water or on the beach. Movement of the bail may actuate the exploder and fire the charge, and movement of the torpedo itself may cause the engine to turn over a few revolutions, driving the tor-pedo forward on the beach. This too, may actuate the exploder, firing the charge.

Figure 33 – The aircraft and PT boat launched Type 91 torpedo.