North American PBJ-1K - USMC, Korea 1950-1953 (Finished, page 4)

[jcf]

The 75mm cannon of the B-25G/H was manually loaded and was neither accurate
nor effective. It didn't last long in service and was pulled and replaced with two
more .50 M2. The poor loader also had to sit sideways. Rockets are more effective
and in the Korean War situation you're looking at accuracy would be largely
irrelevant.
The standard 75mm M48 high-explosive round contains 1.5lbs of TNT, the 5"
HVAR 7.6lbs of TNT or Composition B. A single HVAR is equivalent to five shots
from the cannon. Guess which one is more effective. It didn't actually require
a "really good pilot" to use the HVARs most efficiently, it was a matter of teaching 
them how to make the best use of the rockets, paying attention rather than superior
flying skills.
The P-38, PBJ-1 and PV-2 used the 5" HVAR at times in the last year of the war.

Wartime report and photo of loader.
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[Wardukw]

Would they keep the large cannon if they were carrying rockets?
I know and agree that 'more is better', but thinking of the weight saving.
Carry a slew of rockets on P-38 style 'Christmas Tree' launchers and once they're sent on their way, you have a performance increase and less weight for more fuel economy.

Just my .02 Pacific Pesos...

I was trying to weigh up whether rockets or cannon would be better.  I'll have a look at what those Christmas tree launches look like now.
The pro's of the 75mm for me are that there are at least 20 rounds, potentially more. And maybe more accurate with a dedicated weapon sight.
Pro's of rockets. Lighter and can fire in a volley.

I'd be looking more towards the 75 matey...the rockets which the P-38 uses were not all that powerful where as the 75 could use AP and HE rounds and I'm pretty sure WP rds too .
Also the gun is much more accurate than the rockets ..the rockets ..which are probably HVAR rockets were very good ..no doubts about that but only in the hands of very experienced pilots ..fact they were deadly ..in the hands of not so experienced..not that good ..the cannon tho ..much less chance of wasted ammo ..sleaker aerodynamics and less weight as those HVAR's weighted like 130 lbs or 61 kgs each and ya only get ten per wing .
If ya did the math ..which I ain't 👍..the gun will do more accurate shooting unless you've got a very good pilot behind the stick to use rockets .
Oh you could also carry spare 75mm ammo inside to the plane if needed 😉

SOLD!!

75mm gun, clean outer wings, drop tanks on inner wings.... maybe bombs, napalm or fuel in the bomb bay??

I shall take those 50 points with pride! Cheers 

Matey it all depends what you want this to do ,,whats it's main mission ,,if it's say a ship hunter/killer then bombs and machine guns are great ..napalm is more for ground attack on land with trees and the like ,, but a B-25 is not a plane i'd like to drop napalm from ,,it's mo where as maneuverable as a fighter and ya gotta get real low to use it effectively ,,if yours going for ground attack ,,strafing sort of work then parachute bombs and machine guns ..lots of machine guns ,, 50cals are brilliant at making thing's fall down permanently and parachute bombs enable the plane to drop are very low altitude and not get any damage from their own bombs ,,no good for ships tho as they keep moving most of the time 
One thing i was thinking about to give you more guns is something you said about removing the upper turret ,,,,yep your gonna loose guns but increase your aerodynamics ,,so better range .,,.,hows this for an idea ...the upper remote turret from a P-61 Black Widow  ??
Its very aerodynamic ,,as long as you don's turn it ,,the P-61 didnt like that  ,,so make it a fixed forward firing weapon only ,,thats 4 50cals replacing 2 50cals and a turret system too . 
I have read reports and books about the amount of machine guns the crews would mount on their B-25's and mate some of the numbers are mental ,,14 seems to be a common number but there was some planes with more than that ...one bird i read about had this load out ,,8 in the nose ...two on each side with the side mounts ,,two more in gun pods under each wing plus the upper turret ..thats 18 forward firing 50 caliber machine guns ..i'm not a hundred percent sure but i'm sure there was others with more than that   

[jcf]

Of course there's always "Tiny Tim".
11.75" Tiny Tims being loaded on Marine Corps PBJ-1, Iwo Jima, 2 August 1945.


Douglas AD-1 circa 1946, 10 HVAR and two Tiny Tim

[RAFF-35]

My original notes for this build were;

North American PBJ-1K. Sub hunter, anti shipping, close air support, SAR. US Navy, USMC. Re-engined to use Pratt & Wittney R2800 double wasp for maintenance commonality with other aircraft. Belly mounted search radar, r/c gun turret. Deleted rear gunners position. Guns removed from waist blisters but windows retained for S&R role. Updated aiming systems. Wing tip tanks. Rocket rails. Wings strengthened. Folding wing mechanism. Arrestor hook. Gun exhaust gas vents. Squared wing tips allowed the ailerons to be extended by one foot.
Upgraded T15E1 M10 75 mm cannon with autoloader originally designed for the T22E1. Could fire 20 rounds per minute.
Crew-4: Pilot, navigator/radar operator, flight engineer/radio operator, waist gunner/ observer.

From this list, I think I'll change the tip tanks to drop tanks and potentially move the radar to the wing instead? Keeping the hard points on the wings depends entirely upon whether I have any suitable rockets in the stash.

[RAFF-35]

Of course there's always "Tiny Tim".
11.75" Tiny Tims being loaded on Marine Corps PBJ-1, Iwo Jima, 2 August 1945.


Douglas AD-1 circa 1946, 10 HVAR and two Tiny Tim

I'd love to mount the Tiny Tim's plus HVARs, but unfortunately, I don't currently have any I don't think 

Regarding your previous post, you are an absolute wealth of technical information!! My issue is that it kinda debunks the concept of a big aircraft gun and I've already started with the B-25K kit. Unless...... there's a smaller caliber, higher firing rate cannon that would be better than machine guns and have more rounds + greater accuracy than the HVARs? But then that would lose effectiveness against shipping and bridges and stuff 🤔

[Old Wombat]

You could go 40mm Bofors for smaller-calibre, higher ROF, or you could go right over the top with a 105mm Howitzer M3 (or, if you decided to go British or Australian, a 25-pounder).

[NARSES2]

Never seen an AD-1 with Tiny Tims, but there's something about that photo that doesn't gel to me. Not sure what it is 

[zenrat]

...Douglas AD-1 circa 1946, 10 HVAR and two Tiny Tim

Interesting to note the stars on the fuselage sides are painted under the airbrakes as well as on the outside.


B-25 night fighter equipped with radar and armed with a 75mm gun could have proved effective against Goering's great air fleets of Amerika Bombers should the war have gone on to '46.

[RAFF-35]

You could go 40mm Bofors for smaller-calibre, higher ROF, or you could go right over the top with a 105mm Howitzer M3 (or, if you decided to go British or Australian, a 25-pounder).

Oooh that's a good suggestion,  I'll do some more research into that idea 

[Old Wombat]

Never seen an AD-1 with Tiny Tims, but there's something about that photo that doesn't gel to me. Not sure what it is 

I've seen that photo before, Chris, many years ago, in a book (can't recall which one - I've read a lot of books over the years), but probably on the AD-1/A-1 Skyraider (in my Top 5 Post-WW2 Aircraft).


Ah! Here's the wiki page with the origin of the photo: https://commons.wikimedia.org/wiki/File:Douglas_AD-1_Skyraider_armed_with_rockets_c1946.jpg

[NARSES2]

Thank you Mr Wombat    There was something about it that made my brain go "eh ?" Now I can sleep tonight 

[jcf]

Based on your notes basically what you have is an AJ-1 Savage with guns, and you'd
need something that size to carry all of what you propose.

As to your cannon poll, none of them would fit in the B-25 in the one hole available,
where the 75 was mounted. All of those on your list are too big, and too heavy and
they'd be just as innacurate as the 75. There's a reason why all of the large caliber,
high velocity forward firing cannon experiments were either a flop or had meh results.
Including the vaunted Mosquito Tsetse, it's effectiveness has been overblown. Also I've
been in a B-25, it's tiny and cramped. If you want to increase the weight of what's
hitting your target, with more impact and a decent rate of fire, then a bunch of 20mm
cannon makes more sense. It's also why the USN dropped the .50MG and went to the
20mm cannon as the standard going forward. The USAAF/USAF stuck with the .50 for
a few more years but the Navy said no thanks.

AJ Savage, it's about 10' longer than a B-25 but the span is only about 4' greater,
without the tip tanks, even with the larger fuselage.
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[RAFF-35]

Based on your notes basically what you have is an AJ-1 Savage with guns, and you'd
need something that size to carry all of what you propose.

As to your cannon poll, none of them would fit in the B-25 in the one hole available,
where the 75 was mounted. All of those on your list are too big, and too heavy and
they'd be just as innacurate as the 75. There's a reason why all of the large caliber,
high velocity forward firing cannon experiments were either a flop or had meh results.
Including the vaunted Mosquito Tsetse, it's effectiveness has been overblown. Also I've
been in a B-25, it's tiny and cramped. If you want to increase the weight of what's
hitting your target, with more impact and a decent rate of fire, then a bunch of 20mm
cannon makes more sense. It's also why the USN dropped the .50MG and went to the
20mm cannon as the standard going forward. The USAAF/USAF stuck with the .50 for
a few more years but the Navy said no thanks.

AJ Savage, it's about 10' longer than a B-25 but the span is only about 4' greater,
without the tip tanks, even with the larger fuselage.
You cannot view this attachment.

Do you not think a modified Bk.5/ Mauser 214A would fit in that gap? 😬
The Bk.5 (as standard) weighed only 540kg and had an overall length of 4.35m (the barrel would be trimmed down a bit for this application). It could fire 45 rounds per minute at 1200m/s
The Mauser (as standard) weighed 718kg and had an overall length of 4.16m (practically pocket sized ). It had a rate of fire of 150 rounds per minute with a muzzle velocity of 920m/s.

I did not realise the Savage was that big! It looks like it should be smaller than that 

[RAFF-35]

The gun should surely fit in this gap??

[RAFF-35]

Here are some photos of how the build is progressing, including the new gunner's position with his periscope station. Also note at this stage, smooth engine cowlings to give that R2800 appearance, General Electric gun turret, deleted rear gun position, and squared-off wing tips.