Senior Chief Torpedoman’s Mate (Submarines) Robert F. Marble, USN (Retired) contributed this short article on the operating principles of the wet-heater engine used in the Mark 14 torpedo, as well as a brief footnote on how a technical problem with the Mark 13 (air dropped) torpedo was solved.)

The combustion pot (chamber) is constructed of forged steel and hydrostatically tested at 1500 psi and located in the midships section of the torpedo. A pneumatically “fired” black-powder igniter is screwed into the top of the combustion pot, with a 3/8″ copper tubing line attached to it, coming from the starting/reducing valve body located in the afterbody. Fuel and water whirling-spray nozzles are also screwed into the combustion pot, adjacent to the igniter, with 3/8″ copper tubing lines from their respective tanks, which are located just aft of the air flask.

When the starting valve lever is “tripped” by the forward movement of the torpedo in the torpedo tube, all sorts of things happen.

1) The 2,800 psi air from the air flask is sent to the gyroscope spinning mechanism, which gives the gyro wheel its initial spin up to 20,000 rpm. When this speed is achieved, the spinning mechanism is disengaged from the gyro wheel and is sustained at this speed for the duration of the torpedo’s run by a small 125 psi air reducer located on the gyro housing in the afterbody.

2) 2,800 psi air is directed to the starting/reducing valve body, and the starting piston is lifted, permitting 2,800 psi air to the reducing valve, where it reduces it to a working pressure of 450 psi.

3) Reduced air to the igniter “fires” it, rupturing a blowout seal at its working end, converting it to a “torch.”

4) Fuel enters the combustion pot, followed by the water, and is converted into a fine whirling mist.

5) The 450 psi air from the reducing valve also enters the combustion pot and creates high-pressure steam, which is directed to the turbine gate-valve assembly, mounted on the aft bulkhead of the midships section. Depending upon the speed setting desired (low, intermediate or high) the speed setting mechanism adjusts the gate valve to suit the speed setting.

6) This steam spins the two counter-rotating turbine wheels, driving the two counter-rotating shafts through a “main engine” (actually a differential transmission) to obtain propulsion. The expended steam leaves the turbines and is routed to the exhaust valves mounted on the after bulkhead of the afterbody by thin, large-diameter exhaust tubes. After the exhaust gases and smoke (from the hot-running torpedo oil) pass through the exhaust valves, they exit through the holes in the two outer propeller shafts and out the tail of the torpedo.

Mark 13 Aerial Torpedo Problem and Solution

The Mark 13 aerial torpedo is a single-speed torpedo and has no gate-valve or speed-setting provision. It had, however, a serious problem during startup. Some pilots were launching the MK 13 at altitudes up to 800′ and, upon release, the torpedo started up immediately. The heat created by the combustion pot, and lack of “load” on the propellors, caused the turbine wheels to overspin, fly through the afterbody, and self-destruct.

A simple “fix” was the answer to this problem. It consisted of a small brass wing-like blade (1″ X 1″) pivoted at its large end (positioned at the bottom of the midships section), to act as a cam to trip the “trip-valve” when it entered the water, permitting air pressure to “fire” the igniter.

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