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ť Forum Category: PT Boats of WWII
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ť Forum Name: PT Boats - General
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ť Topic: MK-34 Torpedo Director PT-315 Jan '45 Miami
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This photo of PT-315 taken during tests of the MK-34 Torpedo Director down at the Naval Training Station, Miami in January 1945. I have not been able to find anything on what the MK-34 direct looked like or if it was tied into the SO-3 radar. Close up photo may be the torpedo director. Photo from the PT Boat Museum's collection.

Posted By: Andy Small | Posted on: Dec 28, 2025 - 12:14pm
Total Posts: 273 | Joined: Nov 20, 2013 - 9:04pm

It is really hard to see any details to make any sort of guess. It still is a very interesting idea! To use Radar incorporated into the torpedo aiming sight.

Jerry Gilmartin
PT658 Crewman
Portland OR

Posted By: Jerry Gilmartin | Posted on: Jan 12, 2026 - 11:35am
Total Posts: 1516 | Joined: Oct 8, 2006 - 11:16pm

Andy,

A few thoughts on the subject, while not being able to provide a definitive answer.

Spinning the clock back a year, to July 1944, in MTB RON 29 action report number 2, Stanley Barnes makes commentary about the MK 31 torpedo sight. Based on the comments I can infer that the MK 31 was a lead angle indicator type of sight. This would be similar in function to the Mk 14 gunsight. A self contained trigonometric calculator that would provide the crew with an idea of the angle the boat needed to be to the target. Barnes indicates challenges from the fact that the crew needed to estimate the target speed and there was no way to input the target and PT boat true course into the sight.

Back to the MK 34 sight. If it was based on the MK 31 it is most likely an improved version. Much like the Mk 15 gunsight was an improved version of the MK 14 sight. In which case you will not find a connection of the sight to the SO/SO3 radar. If you have photographs/drawings of the sight, one clue to look for that would indicate a connection would be multi-pin BNC type connectors on the casing. These should not be confused with a power cable cable to the device. Conversely the radar set would need to provide an output connector to the gun sight.

Setting the physical connection aside, the radar inputs are just that. For the device to obtain value from these inputs it would need to calculate the relative motion between the target and the boat. The sight would also need to be able to calculate future position of the target at the time the torpedo arrived. These were calculations performed by the TDC on submarines and destroyers. The TDC was a rather large heavy power hungry analog computer, incompatible for use on small boats. There was no way in 1944/45 to pack even a subset of the TDC into the small form factor of a device such as the MK 34 sight. At best the sight could function as another input sensor to a TDC like device. In this context I do not see the value of creating a physical connection between the MK 34 sight and the boat's radar.

But, I could be wrong. You may want to head up the road a bit to Waltham. The NARA facility there holds the design records for the SO/SO3 radar. I would look for a drawing of the box cover or the electrical schematic to see if there are allowances, such as BNC connectors, for an output to other sensors/electrical devices.

Bill

Bill Smallshaw

Posted By: smallwi | Posted on: Jan 23, 2026 - 8:31am
Total Posts: 156 | Joined: Jun 21, 2007 - 3:02pm

Hi Bill,
Just so as we are all on the same page here, this is a photo of our Mk31 Torpedo Aiming Director that you are referring to. I don't see how it can be "modified" to allow inputs from a radar set? Where and to what would you attach these inputs to? It doesn't make sense to me!

Jerry Gilmartin
PT658 Crewman
Portland OR

Posted By: Jerry Gilmartin | Posted on: Feb 6, 2026 - 5:42pm
Total Posts: 1516 | Joined: Oct 8, 2006 - 11:16pm

Andy,

Digging today at NARA I came across correspondence in early1947 from BuShips that the Navy planned to do testing integrating the Mark 33 torpedo director with the SO-5 radar. The Eclipse Pioneer Co. of Teterboro, NJ was performing the integration work between the torpedo director and the radar. This testing was done aboard PT 616.

The tests were to have been completed in late 1947. I did not find any documentation related to the end results of the test.

Bill

Bill Smallshaw

Posted By: smallwi | Posted on: Feb 11, 2026 - 6:19pm
Total Posts: 156 | Joined: Jun 21, 2007 - 3:02pm