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Forum Category: PT Boats of WWII
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Forum Name: PT Boats - General
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Topic: 20mm Fixed Mount Training Aid for Mark 50 Launchers
http://www.ptboatforum.com/cgi-bin/MB2/netboardr.cgi?cid=101&fid=102&tid=5281

In the Bureau Ordnance, DoN Publication “U.S.Navy Bureau of Ordnance in World War II”, they address that the BuOrd contractors sent to the Philippines area (in December 1944) to install the new Mark 50 launcher 5” spin stabilized rockets noted that this system required extensive training to realize the potential of this armament. The supply of rockets was “marginal”, at best and remained critical well into 1945, so “their use as a training aid was out of the question, so some special training device was necessary for the success of the program.” The solution was to mount a fixed 20mm on the bow of each PT that was then wired for electrical firing on the signal that ordinarily activated the rocket firing. When mounted correctly, the fire control problem was the same for both weapons, so this became a great training aid. This device soon turned into an actual weapon where both launchers and the fixed 20mm were fired simultaneously.

So, has anybody heard about this or have any supporting photographs? It seems this was only done in the Philippine theater, so not something directly coming out of Elco or Higgins.




Posted By: Andy Small | Posted on: Dec 3, 2023 - 7:27am
Total Posts: 266 | Joined: Nov 20, 2013 - 9:04pm

Here is PT 596 from RON 40 the boat arrived at Samar, Philippine Islands, in the summer of 1945.

pcF1Z.jpg

Here is a close up of the MK 50

pcMPa.jpg

pcamf.jpg
pclej.jpg



Posted By: Travis B | Posted on: Dec 3, 2023 - 10:13am
Total Posts: 129 | Joined: Nov 23, 2019 - 10:11am

Thanks! Looking for this fixed bow mounted 20mm they mentioned or any additional info on this in the field setup. I have a good amount of photos of the standard Mk-50 launchers.



Posted By: Andy Small | Posted on: Dec 3, 2023 - 10:44am
Total Posts: 266 | Joined: Nov 20, 2013 - 9:04pm

This is a portion of what the publication says...

pcsU6.jpg



Posted By: Andy Small | Posted on: Dec 4, 2023 - 3:09am
Total Posts: 266 | Joined: Nov 20, 2013 - 9:04pm

Hi Andy,

This is the only thing I've been able to find so far. Not much of a pic, I know, but it appears* to be another 20mm Oerlikon directly behind the 37 mm, with the forward port 20mm visible as well. The former has what appears to be an AA handle on it, though, so I don't know if it's one of the fixed training ones or if they just threw an extra one on, and/or maybe found a way to fix that in place for rocket practice. I don't know, only guessing.

https://www.ibiblio.org/hyperwar/USN/CloseQuarters/img/PT-p433.jpg



Posted By: Joe Reese | Posted on: Dec 6, 2023 - 7:58pm
Total Posts: | Joined: Unregistered

Thanks Joe, I believe you found it! I must have skipped right by that photo millions of times and never noticed it!

pcIo5.jpg



Posted By: Andy Small | Posted on: Dec 7, 2023 - 10:32am
Total Posts: 266 | Joined: Nov 20, 2013 - 9:04pm

Closer view from the Naval History and Heritage Command site.

pcRnS.jpg



Posted By: Andy Small | Posted on: Dec 7, 2023 - 10:42am
Total Posts: 266 | Joined: Nov 20, 2013 - 9:04pm

Hi Andy,

I'm kind of surprised. I was searching for something on the center line, never thought about it being mounted right next to the launchers.

This makes me wonder about the forward center 20mm. Could this boat maybe have had the 4.5 rockets first, and moved their 20mm to the center line to be out of the way, then got a refit with the 5 inch?



Posted By: Joe Reese | Posted on: Dec 7, 2023 - 10:50am
Total Posts: | Joined: Unregistered

Andy and Joe;

Funny, I have looked at this photo a million times over the past 30+ years, saw both 20MM ‘s but never thought twice about it. I believe this is PT 525. RON

Take Care,
TED



Posted By: TED WALTHER | Posted on: Dec 7, 2023 - 12:21pm
Total Posts: 3071 | Joined: Oct 16, 2006 - 7:42am

It was a common place for the extra 20mm mounts, so maybe it's all just a WAG at this point. I'm going to keep looking since I too was looking for something right on the bow.



Posted By: Andy Small | Posted on: Dec 7, 2023 - 1:04pm
Total Posts: 266 | Joined: Nov 20, 2013 - 9:04pm

I do not see any type of electric firing mechanism on that 20mm cannon in the photo. Wouldnt the set up require a remote trigger for the 20? The normal trigger is on the left side of that box on top rear of the weapon.

Jerry Gilmartin
PT658 Crewman
Portland OR

Posted By: Jerry Gilmartin | Posted on: Dec 7, 2023 - 1:23pm
Total Posts: 1486 | Joined: Oct 8, 2006 - 11:16pm

Plus I just noticed that neither of those 20mms have a magazine mounted on them! If it was being used for sighting in the rockets do you suppose it might be loaded with a magazine?

Jerry Gilmartin
PT658 Crewman
Portland OR

Posted By: Jerry Gilmartin | Posted on: Dec 7, 2023 - 1:27pm
Total Posts: 1486 | Joined: Oct 8, 2006 - 11:16pm

I'm rather curious about what those objects just forward of the 20mm are.

Al Ross



Posted By: alross2 | Posted on: Dec 7, 2023 - 6:47pm
Total Posts: 994 | Joined: Oct 30, 2006 - 8:19pm

Al;

The objects on the deck look like extra ammo cans in a specially built rack so they could be secured while underway. To me they look same as the ammo can at the base of the 37MM.

Take care,
TED



Posted By: TED WALTHER | Posted on: Dec 8, 2023 - 1:18pm
Total Posts: 3071 | Joined: Oct 16, 2006 - 7:42am

I would agree with Andy, there is a need to keep looking. Reasonable call that this photograph might be a representation. But there does not appear to be any form of sight, nor transducer, attached to either mount that could have been used to direct the rockets.

Bill Smallshaw

Posted By: smallwi | Posted on: Dec 9, 2023 - 12:34pm
Total Posts: 141 | Joined: Jun 21, 2007 - 3:02pm

Andy and Joe;

I believe this is PT 525.

Take Care,
TED



Posted By: TED WALTHER | Posted on: Dec 12, 2023 - 5:29pm
Total Posts: 3071 | Joined: Oct 16, 2006 - 7:42am

Al;

The objects on the deck look like extra ammo cans.

Take care,
TED



Posted By: TED WALTHER | Posted on: Dec 12, 2023 - 5:29pm
Total Posts: 3071 | Joined: Oct 16, 2006 - 7:42am