Bf 109G armament options.

[Johnny .45]

Bf 109G's were armed with only three guns: the two 13mm MG 131 machine-guns in the cowling, and a single 20mm MG 151/20 or 30mm MK 108 firing through the propeller hub. The MG 151 was the weapon that replaced the two wing-mounted MG FF cannons of the Emil version.
The fact that it was a single gun rather than 2 wasn't as important as it seems, since a centerline-mounted gun is far more accurate and effective than a wing-mounted gun, and the MG 151/20 enjoyed a greater rate-of-fire and muzzle velocity than the MG FF. The superior weapon/mounting made a single MG 151 more effective than 2 MG FF's.
However, the Luftwaffe soon found that the Bf 109/MG 151 combination was sadly lacking in bomber-destroying power. In response, later Gustav's were fitted with a single 30mm MK 108 in place of the MG 151. This fired far more powerful shells that could easily bring a B-17 down, but it had very low muzzle velocity, which required the fighter pilot to get very close before firing. It also traded anti-fighter capability for anti-bomber capability...although a single 30mm hit on an enemy fighter would invariably destroy it, the slow projectile and extreme drop made hitting the enemy at all an uncertain thing.
Now, taking the German tendency to create "modular" armament for its' fighters into account, I have to wonder whether the two weapons were interchangeable. Could one remove the MG 151 from a Gustav and install a MK 108, or vice versa? Or were MK 108 planes built that way in the factory? It would seem to make sense to build to fighter to easily hold either weapon, like a "universal" wing on a Spitfire. I'm curious, since I can't see any obvious relation to the specific type of plane and it's weapons; I've seen G-6's that are armed with 20mm, and G-6's with 30mm guns. And G-14's carried MG 151's, even though the version came after they began using 30mm's in most planes.
Anyone know anything about this? If a specific type, like a Bf 109G-6 or G-8 can be armed with either gun, than it must be possible to interchange the guns. If it was built to hold one type of gun "permanently", than why wouldn't they denote it's armament in the planes designation? I mean, it would make more sense to title an MG 151-armed plane as a "G-9" and a MK 108-armed plane as a "G-10". Or at least put a suffix onto the designation, i.e. "Bf 109G-6(A)" or "Bf 109G-6(B)".
Oh well, just curious.

[Nick Beale]

Johnny, you do type a lot of words before you get to the actual question!

The simple answer (as far as that's ever possible with a Bf 109) is that there was a special designation: a Bf 109 G-6/U4, G-14/U4 or G10/U4 carried a 3 cm MK 108 instead of the 2 cm MG 151.

U stands for «Umrüst-Bausatz» or re-equipment set and denotes an equipment change built in at factory level.

Incidentally, there wasn't much point in putting an MK 108 in a G-8 since it was a dedicated reconnaissance model. If the armament was altered on that machine, it was to reduce it (commonly to a singe MG 151 and no machine guns).

There's plenty of material on Tony Williams' site (and in his books) that you'd probably find helpful.

[the_ivan]

MG 151/20 and MK 108 used different engine gun mounts (Motorlafette, or MoL), that weren't interchangeable. As Nick said, aircraft with the MK 108 were designated with the suffix /U4.

Towards the end of the war there were some meetings for developing an universal gun mount that would accept different weapons (in service and in development).

[Johnny .45]

Originally Posted by Nick Beale

Johnny, you do type a lot of words before you get to the actual question!

Incidentally, there wasn't much point in putting an MK 108 in a G-8 since it was a dedicated reconnaissance model. If the armament was altered on that machine, it was to reduce it (commonly to a singe MG 151 and no machine guns).

LOL, yes, I do like to hear myself talk, I guess. Or, "read myself typing", rather?
I figure stating the obvious can be useful for those who are just dropping in casually.
As for the G-8, I just used that as an arbitrary title...I don't really know a lot about all the different Bf 109G versions...there's too many of them!
I commonly hear that the 109's were (when possible) used to take on the escort fighters, while the Fw 190's were supposed to take on the bombers. I know that wasn't always possible, and I assume that those roles were assigned by virtue of the two fighters armament (or lack thereof), since the Fw always seemed to be a better dogfight (IMHO). Anyway, what does a 30mm-armed Bf 109 do against another fighter? I can't imagine it would be easy to shoot a fighter down with an MK 108.
So, now for the question(s)! Does anyone know how many of each type was built? Meaning MG 151 vs MK 108-armed Bf 109's, that is. And was a 30mm-armed fighter generally assigned to go after bombers, or did they actually try to take on the fighters (as official tactics)? It seems to me that the 30mm version was more of a stop-gap bomber-destroyer top fill in for the Fw 109 at higher altitudes, where the Fw lost power.

[Nick Beale]

Originally Posted by Johnny .45

I don't really know a lot about all the different Bf 109G versions...

There are many books that will help you, as well as web resources.

[Harold Lake]

Establishing how many Bf 109 Gs were equipped with the MK 108 versus the MG 151/20 would be a very tedious and time-consuming exercise, so it is unlikely you will find this sort of data in-print. In addition, I can't recall any respected author claiming aircraft with the larger caliber weapon would have been restricted in their choice of targets. But it is common knowledge many experienced pilots found the MK 108's blinding muzzel flash to be very distracting; especially in evening or night ops. Fighter units took what they were issued and it was up to their commanders to make the best use of their hardware vis-a-vis mission and choice to targets.

Hal

[harrison987]

Actually...though it is a hard conversion, the MK108 could be installed in a regular Me109 that was equipped with the 151/20. The main difference was the mount that was located on the engine itself.

The MG151 was mounted to the engine, AS WELL as on an MG151 Starre Lafette that was attached to the cockpit floor. So there were 2 main attachment points.

The MK108 ONLY mounted to the engine (with no secondary mount in the cockpit).

The ground crew would have to remove the internal 151 mount, as well as the one on the engein...then replace the engine mount to accept the MK108

Every Me109 from the G2 onwards had 2 different holes in the floor for the (ejection chutes/feeds) for the MG151 AND the MK108. So a conversion could be done.

Whether one was actually converted is a different story, however.

Mike