Pom pom with director Mk IV vs Bofors 40mm with Mk 51

[wmh829386]

Pom pom director Mk 4 is a very complicated director that integrated Gyro rate unit (GRU) and a Type 282 radar. There are 8 members on the director sight itself: 1 Officer, 3 rate followers, trainer, layer, GRU operator, range taker.

On the other hand, Bofors in USN service mostly relies on a Mk 51 director. A simple gyro sight with one operator and a talker.

Is there any evidence that the elaborate Pom pom director with Radar is actually effective when comparing with the simple Mk 51 director?

And overall, how would a Octuple Pom pom compare vs quad bofors with their respective directors?

[dunmunro]

Pom pom director Mk 4 is a very complicated director that integrated Gyro rate unit (GRU) and a Type 282 radar. There are 8 members on the director sight itself: 1 Officer, 3 rate followers, trainer, layer, GRU operator, range taker.

On the other hand, Bofors in USN service mostly relies on a Mk 51 director. A simple gyro sight with one operator and a talker.

Is there any evidence that the elaborate Pom pom director with Radar is actually effective when comparing with the simple Mk 51 director?

And overall, how would a Octuple Pom pom compare vs quad bofors with their respective directors?

There's lots to consider about this, including the fact that the RN developed a similar director to the Mk 51, which was called the Simple tachymetric Director. In theory the Mk4 was superior due to the Type 282 radar, since it provided precise radar ranging. OTOH, the superior ballistics of the Bofors gun compensated, to some extent, for the simple ranging techniques employed by the Mk 51.

The Octuple mount, when fitted with RPC (remote control) from mid 1942 onward, could be entirely controlled by the Mk4 with no need for a crew on the mount, since each of the 8 barrels had it's own ~150 rnd magazine.

[wmh829386]

Is there any information on how widespread the installation of RPC pom pom mounts is? I suspect a lot will be retrofitting existing mounts, but I haven't come across any records.

Also, even though type 282 radar is pretty common, there seems to be very few mentions on its effectiveness on action reports. Have you come across any?

[dunmunro]

Is there any information on how widespread the installation of RPC pom pom mounts is? I suspect a lot will be retrofitting existing mounts, but I haven't come across any records.

Also, even though type 282 radar is pretty common, there seems to be very few mentions on its effectiveness on action reports. Have you come across any?

All new cruisers and fleet carriers from completed from mid 1942 or so had Mk IV directors with RPC control. Cruisers and larger ships that were given extensive refits from late 1942 also gained RPC for Pom-poms and 4in twin mounts. During their engagement in the Bay of Biscay, Glasgow and Enterprise had been given RPC for pom-poms and 4in guns. Fortunately this was just about when daylight air attacks on RN ships fell off considerably but consequently data on Mk IV director performance is scarce. During Pedestal Victorious had 5 octuple pom-poms modified to use 'joystick' control for one man training/laying control of the mounts, and the 6th mount was given Mk IV control. Unfortunately the director was wooded during most of the short range attacks:

Pom Pom Control.
16. Five pom poms were aimed locally using the joysticks, and one was
in director control. The joysticks are considered a big improvement on
the previous system of divided aiming by the layer and the trainer and are
liked. The aiming of all guns appeared to be good.
17. It was unfortunate that the one pom pom (S4) in director control had
to be restricted in its arc of training because of Hurricanes being kept on
the Flight Deck abaft the Island, and also that most of the pom pom firing
took place in the dusk attack on Tuesday, when speed in picking up and
shifting target was at a premium. On several occasions targets were picked
up by the gun before the director and the Officer at the gun opened fire
in local control. Two or three accurate bursts (in director control) were
reported by the Officer stationed at this gun, particularly one at a Ju.88
on the starboard beam on Tuesday evening. This was the aircraft which
subsequently crashed on the starboard bow. On Wednesday all targets
were outside range and no definite conclusions as to the relative
advantages of the director and the local joystick control can be drawn
from this action …

I'll hunt around for more info on type 282. However Type 283, which was very similar was used for ABU control quite successfully.

[wmh829386]

During Pedestal Victorious had 5 octuple pom-poms modified to use 'joystick' control for one man training/laying control of the mounts, and the 6th mount was given Mk IV control.

I am pretty surprised that 5 octuple pom-poms uses local one man control. As I believe as designed, director positions are provided for all octuple pom-poms.
But I remember reading earlier reports, I think from Illustrious, that director is almost useless without RPC because the crew kept looking at the attacking plan rather then following the pointer.

Regardless, I suppose at that point, only the ring sight is used on mount?

[dunmunro]

During Pedestal Victorious had 5 octuple pom-poms modified to use 'joystick' control for one man training/laying control of the mounts, and the 6th mount was given Mk IV control.

I am pretty surprised that 5 octuple pom-poms uses local one man control. As I believe as designed, director positions are provided for all octuple pom-poms.
But I remember reading earlier reports, I think from Illustrious, that director is almost useless without RPC because the crew kept looking at the attacking plan rather then following the pointer.

Regardless, I suppose at that point, only the ring sight is used on mount?

Illustrious and Victorious were originally fitted with Mk III directors. Pom-pom mounts began to be fitted with USN Mk 14 gyro gunsights, probably in 1942, but I don't know the status of the mounts used during PEDESTAL. The one man joystick control was engineered by the Mediterranean Fleet and then adopted in general by the RN.

[wmh829386]

Illustrious and Victorious were originally fitted with Mk III directors. Pom-pom mounts began to be fitted with USN Mk 14 gyro gunsights, probably in 1942, but I don't know the status of the mounts used during PEDESTAL. The one man joystick control was engineered by the Mediterranean Fleet and then adopted in general by the RN.

Seems like Mk III director was not a success. In Mk II and Mk III, the control office uses the Control Office Forward Area Sight (C.O.F.A.S.), which essentially is a one man control (given the layer and trainer are not too far off.

https://www.armouredcarriers.com/gunner ... ary-7-1941

But the is a bit of technicalities about the Mk IV that bugs me.

1. Can the control office apply correction manually through his sights?
2. Can fire be opened from the director before rate from GRU is established?

[dunmunro]

Illustrious and Victorious were originally fitted with Mk III directors. Pom-pom mounts began to be fitted with USN Mk 14 gyro gunsights, probably in 1942, but I don't know the status of the mounts used during PEDESTAL. The one man joystick control was engineered by the Mediterranean Fleet and then adopted in general by the RN.

Seems like Mk III director was not a success. In Mk II and Mk III, the control office uses the Control Office Forward Area Sight (C.O.F.A.S.), which essentially is a one man control (given the layer and trainer are not too far off.

https://www.armouredcarriers.com/gunner ... ary-7-1941

But the is a bit of technicalities about the Mk IV that bugs me.

1. Can the control office apply correction manually through his sights?
2. Can fire be opened from the director before rate from GRU is established?

COFAS = Commanding Officer Forward Area Sight; the ring sight on the Mk II/III pom-pom director, but I think that also pertains to the COFAS on a MkIII or IV HADT (medium calibre AA gun director) so it's easy to get them confused. As has been mentioned, the MkIII pom-pom director's main failing was the necessity of the layer and trainer on the pom-pom mount to follow their pointers, which was problematic in actual combat. The simple ring sight was also not ideal, but a dive bomber or torpedo bomber presents a low deflection target and so the Mk III pom-pom director should be considerably superior to local control on a pom-pom mount that didn't have one man joystick control.

The Mk IV pom-pom mount's GRU could establish rate very quickly so I don't think that was an issue, but the Type 282 radar had to track the same target so that data from the GRU and range could be combined for an accurate rate and that was a potential issue.

HMS Prince of Wales was the first ship to use the Mk IV pom-pom director (with Type 282 radar) in action during Operation HALBERD, and it seemed to work very well there, but by Dec 1941 her Type 282 radars were mostly out of service and the pom-pom mounts were having other issues.

[wmh829386]

Regardless, the Mk IV director need the crew of 8 + radar crew to work in unison, and there will definitely be delays such as

1. trainer and layer to recognise the target selected by CO
2. GRU operator to line up with target and followers to put in the rates
3. Range follower to input range, either from radar or optical RF (the antenna move with the mount, so the time taken for radar range might not be that long)

And it seems like in Mk IV, the officer do not have the means to apply spotting correction?

It seems a bit odd that the Mk IV pom pom director is available in quite some numbers, with a large crew, yet the account of usage is extremely sparse.

[dunmunro]

Regardless, the Mk IV director need the crew of 8 + radar crew to work in unison, and there will definitely be delays such as

1. trainer and layer to recognise the target selected by CO
2. GRU operator to line up with target and followers to put in the rates
3. Range follower to input range, either from radar or optical RF (the antenna move with the mount, so the time taken for radar range might not be that long)

And it seems like in Mk IV, the officer do not have the means to apply spotting correction?

It seems a bit odd that the Mk IV pom pom director is available in quite some numbers, with a large crew, yet the account of usage is extremely sparse.

1) The layer and trainer's sights were aligned with the COFAS so it would be obvious to the CO and the layer and trainer if they were following the wrong target.
2) In later models the COFAS was linked to power control to allow the CO to track the target via the COFAS to ensure that everyone was following the same target; in fact I suspect the GRU joystick would then control the director.

We have to remember that the targets are typically making low deflection attacks directly towards the ship and fire would not be opened before the predicted range was about 2500 yds; at that range, as long as the sights are centred on the target the spread in the pom-pom mount barrels would ensure that the target was within the cone of fire.

The problem is that most RN AA action reports haven't been published and so we're only seeing a tiny proportion what transpired. I know that KGV and Howe reported favourably on type 282/MkIV director control in 1944/45.

[Steve Crandell]

A torpedo bomber would not be flying directly at the ship. There was quite a lot of lead involved.

[dunmunro]

A torpedo bomber would not be flying directly at the ship. There was quite a lot of lead involved.

Yes some deflection, but nothing like that required to engage the same aircraft attacking a different ship.

[Steve Crandell]

A torpedo bomber would not be flying directly at the ship. There was quite a lot of lead involved.

Yes some deflection, but nothing like that required to engage the same aircraft attacking a different ship.

True, but of course you would be trying to do that as well.

[dunmunro]

A torpedo bomber would not be flying directly at the ship. There was quite a lot of lead involved.

Yes some deflection, but nothing like that required to engage the same aircraft attacking a different ship.

True, but of course you would be trying to do that as well.

True, but the pom-pom's SD fuze range was about 2500yds and that limited it's ability to provide area defense unless the attacker tried to overfly the firing ship.

[Steve Crandell]

Well, a circular screen of an HVT would have the screening ships often less than 2,500 yds apart, so well within 2500 yds and attacker would often be trying to fly between the screening ships.