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» Forum Name: PT Boats - General
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» Topic: Curved handle bars Oerlikon
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I'm in the process of adding the curved handle bars to the Oerlikon of my PT 515 model. I wonder when these curved handle bars were introduced on PT boats and whether or not this was originally a field modification.

I take it the handle bars were added to make elevation of the gun easier because the guns were mounted rather low on the deck. The trigger of the gun is not on the handle bars so it seems one hand had to be on the bars and one on the trigger which was located on the gun itself.

Not clear to me if the Oerlikon gun had a single shot option or whether the magazine was simply emptied automatically after having activated the trigger mechanism. Since there were no sights on this type of Oerlikon I take it the gun was more or less handled like a fire hose ?

Arjan

Posted By: Arjan Wiskerke | Posted on: Jul 18, 2019 - 2:06am
Total Posts: 162 | Joined: Dec 22, 2018 - 12:04pm

This should answer all your questions:

Posted By: Jeff D | Posted on: Jul 18, 2019 - 4:00am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

Another question re. the 20 mm Oerlikon...

Did the gun have an adjustable rate of fire? I've seen film of the gun in action on capital ships against Japanese aircraft, and the rate of fire is very rapid, like a machine gun.

I've also seen the gun in a very slow rate of fire, say in the movie "PT 109," and in single-fire mode in another movie ("Thunderbolt and Lightfoot").

I realize the movies are Hollywood fictions (well, fact-based, occasionally fictionalized, in the case of "PT 109"), but, did the Oerlikon have an adjustable rate of fire?

Posted By: Drew Cook | Posted on: Jul 18, 2019 - 4:38am
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am

I believe the gun fired like the .50 cal, no selector switch for auto / single fire, it just fired as long as the trigger was pulled. And again like the .50, sights were available but often not used.

Interesting observation about the method of pulling the trigger when those curved grips were used, I have no clue. Nor do I have any clue about the contraption grips I posted above. :D

I don't think it had an adjustable rate of fire Drew.

Posted By: Jeff D | Posted on: Jul 18, 2019 - 4:45am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

This is the only image I found of a similar setup with the sight in use, on an Elco 80 in Norwegian service:

The sight:

Posted By: Jeff D | Posted on: Jul 18, 2019 - 5:01am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

Thanks so far gentlemen. I noticed that at least some of the Elco PT boats in the Med also had these curved handle bars but it appears the Higgins PT boats in the Med didn't have any fitted to their bow Oerlikon guns.

Regards,

Arjan

Posted By: Arjan Wiskerke | Posted on: Jul 18, 2019 - 8:52am
Total Posts: 162 | Joined: Dec 22, 2018 - 12:04pm

I just found out, the MK1 Oerlikon did have selective fire, semi and full. All other marks from the different country's were full auto only. As slow as they fired, one would think that a skilled gunner could quickly squeeze and release the trigger and only let off one round.

Posted By: Stearman | Posted on: Jul 21, 2019 - 3:10am
Total Posts: 150 | Joined: Nov 1, 2017 - 9:38pm

Thanks, Stearman,

It sure seemed so, from the films I mentioned. The 20 mms in those movies must've been Mark I models.

Posted By: Drew Cook | Posted on: Jul 21, 2019 - 8:27am
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am

I looked in the 20mm Manual found on the HNSA website. It discusses the different Marks. 1,2 and 4
"The Mark 1 Gun was the original type made in Switzerland. The Mark 2 is the improved version made in England and also being made in U. S. A. The Mark 4 Gun is almost identical with Mark 2 except for slightly different manufacturing limits. Both Marks 2 and 4 Guns will be found in service in the U. S. Navy, but eventually only the Mark 4 will be manufactured in this country."
So from this I came to the conclusion that the 20mm cannons used on the PT Boats could not have been Mark 1. I also know that Mark 2 and Mark 4 have only Fire and Safe Positions on their Selector Switches. No Single Fire is possible in this API type cannon. The listed Rate of Fire is 450 rounds per minute.(about 7 rounds/second!) I imagine it can be slower than that but I don't know how you could control single shots, and don't think it possible.

To look for yourself; go to the HNSA Website, [url]https://www.hnsa.org/manuals-documents/ordnance-gunnery-and-fire-control/[/url] 20 MM Antiaircraft Gun, OP 911, 1943, is a Navy service manual for the anti-aircraft gun of choice during the early years of WW II.

Also a movie of a 20mm being shot recently at Stone Mountain Georgia [url] https://www.youtube.com/watch?v=DC4mdAoRfK8&t=44s [/url]

Jerry Gilmartin
PT658 Crewman
Portland OR

Posted By: Jerry Gilmartin | Posted on: Jul 21, 2019 - 2:34pm
Total Posts: 1473 | Joined: Oct 8, 2006 - 11:16pm

Thanks gentlemen ! Interesting footage Jerry, this clearly shows that the gun is mounted so low that sights are of no use when the gun is elevated beyond a certain angle (perhaps sitting on your bum would get you low enough to use the standard sights) .Interestingly this pic shows that the Oerlikon on PT 620 didn't have any sights but it did have both the standard shoulder rests and the curved handle bars :

Regards,

Arjan

Posted By: Arjan Wiskerke | Posted on: Jul 21, 2019 - 11:55pm
Total Posts: 162 | Joined: Dec 22, 2018 - 12:04pm

Sitting on your bum would be about the only way to accurately fire this 37mm. It seems to me to be a good way to maintain a low profile against enemy fire as long as aircraft weren't the main target. It looks like about 30-35 degrees would be the max elevation this setup would be capable of:

Posted By: Jeff D | Posted on: Jul 22, 2019 - 5:23am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

I'm a bit puzzled by the Italeri Oerlikon, its trigger housing and handles are much further forward in relation to the gun carriage than these parts on the real gun (on the real one the rear of the trigger housing aligns with the rear of the gun carriage). I'm afraid some surgery is required to align the rear of the trigger housing with the rear of the carriage. Without these modifications there is simply no room for the curved handle bars.

Regards,

Arjan

Posted By: Arjan Wiskerke | Posted on: Jul 23, 2019 - 2:04am
Total Posts: 162 | Joined: Dec 22, 2018 - 12:04pm

I see what you mean, even the trigger box looks too short. And maybe the whole gun. Good luck my friend, I'm sure you will do an excellent job. Have you looked into aftermarket guns, or maybe a 20mm from another kit?

Posted By: Jeff D | Posted on: Jul 23, 2019 - 3:00am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

Hi Jeff, I bought a set of rather nice 3d RN Oerlikons at Shapeways for my Lend Lease Vosper :

They are quite expensive though and their gun carriage/mount would also require some modifications. It seems there was a truly bewildering variety in the types of Oerlikon mounts and carriages used in WWII. To go short, I think I will simply modify the Italeri gun. After all, this shouldn't be too difficult.

Regards,

Arjan

Posted By: Arjan Wiskerke | Posted on: Jul 23, 2019 - 9:03am
Total Posts: 162 | Joined: Dec 22, 2018 - 12:04pm

I get the impression that the Italeri people mistakenly incorporated some features of this type of British Oerlikon in their gun (different gun-carriage, rear of the trigger housing does not align with the rear of the carriage ). Source IWM :

Arjan

Posted By: Arjan Wiskerke | Posted on: Jul 23, 2019 - 2:48pm
Total Posts: 162 | Joined: Dec 22, 2018 - 12:04pm

Man, oh, man Jerry -- that video is really cool! Thanks for posting the link. That rate of fire is consistent with combat film footage from the Pacific.

So, like I said, I guess the slow "pom...pom...pom...pom" rate of fire in the "PT 109" movie's Oerlikon, and the single-shot in the "Thunderbolt and Lightfoot" movie's gun was - pure Hollywood?

Posted By: Drew Cook | Posted on: Jul 23, 2019 - 3:33pm
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am

Yes apparently pure Hollywood. I read somewhere that the Thunderbolt and Lightfoot Clint Eastwood movie had to use several parts kluged together to make something that looked similar to the 20mm Lahti Anti tank gun that was used in the real bank robbery in upstate New York. The real robber had ordered the gun to be delivered but did not pick it up since it was being watched by the FBI. So he hired his buddy to break into the delivery warehouse and steal the gun at night so the FBI never got to arrest him when he showed up to claim the gun.
Anyway the movie was loosely based on that event. The movie weapon is mostly a 20mm Oerlikon, but it has a 20 round Box magazine on top instead of the normal 60 round drum. The 20 round box was a feature of the Lahti. They also made the gun into a propane gas firing gun for the sound but it was nowhere near as fast firing as the real 20mm Oerlikon.

Jerry Gilmartin
PT658 Crewman
Portland OR

Posted By: Jerry Gilmartin | Posted on: Jul 23, 2019 - 5:18pm
Total Posts: 1473 | Joined: Oct 8, 2006 - 11:16pm

The PT 109 movie 20mm was gas fired. You can see the hoses coming up through the empty shell casing bag.

Also, don't know if you noticed but when CDR. Ritche was firing the 20mm, the magazine kept changing sides it was mounted on. Probably a difference in studio shots and shots on the boat.

Charlie

Posted By: 29navy | Posted on: Jul 24, 2019 - 3:59am
Total Posts: 600 | Joined: Dec 28, 2006 - 3:02pm

Arjan;
Having fired a later model 20MM, I can tell you, other than the MK 4 stern mount, nobody really used the sights. You walk your rounds into the target using tracer rounds. Same with the 37MM. In the photos, see where Jim’s index and middle finger are? That’s the depression trigger, same as in the RN photos.
Those RN 20MM’s look great, why don’t you make a mold and cast them yourself?
Take care,
TED

Posted By: TED WALTHER | Posted on: Jul 24, 2019 - 5:20am
Total Posts: 3059 | Joined: Oct 16, 2006 - 7:42am

Thanks Ted. I only want to modify one Italeri gun and this is a rather simple matter so it wouldn't pay to make molds and casts. Besides, I have often tried to make molds and casts in the past and this proved to be more difficult than I had thought. There were always air bubbles in my casts and I often added too little or too much hardener to both the silicon and resin mix ..... I have found some nice reference close ups of the US 20mm/70 Oerlikon :

http://svsm.org/gallery/20mm_oerlikon?page=1

By the way, in my earlier posts I used the term "carriage" whereas I should probably have used the term "cradle" .

Regards,

Arjan

Posted By: Arjan Wiskerke | Posted on: Jul 24, 2019 - 11:49am
Total Posts: 162 | Joined: Dec 22, 2018 - 12:04pm

Charlie,

I re-ran "PT 109," and I didn't see any gas hoses going through the shell collection bag on the 20 mm. I did see the "cocking wire rope" at the base of the pedestal, which is dark-colored, and sort of looks like a hose...

I did notice the magazine drum changing sides in a Cdr. Ritchie shooting down a "Zero" shot, though. Looks like a flipped/reversed image.

Posted By: Drew Cook | Posted on: Jul 25, 2019 - 1:36pm
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am

You may have already seen this Arjan, it is from the hnsa manual:

Posted By: Jeff D | Posted on: Jul 26, 2019 - 4:03am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

My idea of an excellent addition to a man cave:

Posted By: Jeff D | Posted on: Jul 26, 2019 - 4:11am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

There were different magazine designs, the upper right is what was used on USN guns:

Posted By: Jeff D | Posted on: Jul 26, 2019 - 4:24am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

Charlie

Posted By: 29navy | Posted on: Jul 26, 2019 - 6:06am
Total Posts: 600 | Joined: Dec 28, 2006 - 3:02pm

Nice catch Charlie.

Interesting mount on the twin on display near the museum ship HMCS Haida docked in Hamilton, Ontario. It appears to have a shock absorbing system like the twin .50 Mark 17 mount. The guns seem to have a mix of the British style square section springs and round US style:

Posted By: Jeff D | Posted on: Jul 26, 2019 - 6:31am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

Thanks gentlemen for the really useful reference pics. I bookmarked the HNSA website after Jerry mentioned it. An Oerlikon gun would indeed be a nice addition to a (luxury) mancave. Unfortunately, I can't afford one [:-happy-:].

Regards,

Arjan

Posted By: Arjan Wiskerke | Posted on: Jul 26, 2019 - 8:51am
Total Posts: 162 | Joined: Dec 22, 2018 - 12:04pm

Ok Charlie, I see it now. Looks like you're right. Its too thick for the cocking wire rope. Thanks for the screen shot.

Posted By: Drew Cook | Posted on: Jul 26, 2019 - 12:20pm
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am