by Steve Saunders, July 2001

Two hydrovanes were recently found in a tunnel at Rabaul. The entrance was exposed by heavy rain. Rough dimensions are ~13" diameter by ~66". They were found with some anti-mine hydrovanes, and a small ‘stool’ type cradle is at front left.

This photo shows at right what appear to be ship deck torpedo launch frame or cradle. When I first saw the cradle I thought it may have been an aircraft torpedo launch cradle, but it is solid steel and takes 4-5 grown men to move it! There is some red paint still on the release mechanism. Apparently there are lots more things in the tunnel.

A small hydrovane. How they worked can be seen on this view: a hawser would be attached to the eye and when towed by a minesweeper it would move out sideways from the boat (I assume they would have 2 - one port one starboard), cutting mines free. They usually have a valve somewhere on them to add compressed air or water(?) to set the depth at which they would be neutrally buoyant.

These are very common around Rabaul often used as gate posts and boundary markers. I assume after the war they were recognised as not explosive, so were not removed or dumped at sea, hence so many survived. That knowledge has been lost and now people view them with suspicion, many that came to light after the eruption were removed as 'bombs' They vary in size some being quite large. This one has shrapnel damage, did its hawser hit a mine? Also note the hollow aerofoil shape of the torpedos' wing construction at bottom left of photo.

The 'Stool' like cradle. The width of the gap between the 'ears' is 47cm (18.5"). The up standing lip at the back seems original so it can't have been for a complete torpedo. For working on just the war-head perhaps? Perhaps a large calibre shell cradle, before being pushed into a gun? did the 'stool' sit in a socket on the floor so it could rotate? Note holes at top of vertical ears (for a strap?) If it was a bit bigger and had a lip both ends.

They have a circumference of 108 cm so diameter of 34.3 cm (13.5"). Movable flaps on the vertical stabilisers can be clearly seen on left one and the one left back ground. Also note no hole at apex of tail cone, there is an iron threaded plug in a small hole.

Detail of mechanism in tail cone, central shaft with two brass lock nuts holding a spring against main body. The shaft appears to be solid and is linked by two cams to the vertical stabiliser flaps. Perhaps the spring is to centralise the stabilisers, or is it the plunger for the detonator? ie the spring depressed on impact throwing the pin forward. Where were the fuses in regular torps.? There appears to be no propulsion mechanism, did the thing simply rely on the forward momentum of the aircraft?

Shows the release cradle. I assume the big long tube is the top and the short angle iron the base. In the center there are big pincer like claws for holding and releasing the torp they are 18" wide. These claws would have been opened by the big lever on top or by pulling or pushing a pistol grip at the end of the main round shaft. There are also two horizontal shallow 'c's on the top tube to stop fore and aft swinging of the torp, again they are 18" from horn to horn. The moving parts are held in large '?' shaped divots, like lifeboat divots, joined at the bottom by angle iron and at the top by the main tube. Notice the outward pointing lugs on the upper rear of these '?' shaped pieces.