Notes

1. The M4, M10 and M9

By a publicity effort the American Aircraft Co. (AAC) managed to associate itself with the M4 and M10 series of cannon, and it is sometimes named as its manufacturer. In fact AAC's cannon was far inferior, and never seems to have been used in combat by anyone. The M4 was designed by Browning, and production was undertaken by Colt.
Another source of confusion is that rather frequently, the performance data for the Oldsmobile-produced M9 are listed in tables, creating the impression that this was a standard weapon in US aircraft, or that the performance of the M9 was somehow representative of that of far less powerful and more common M4 and M10 (for example in Ref. [26]). I have found no record of any installation of the M9 in production aircraft, the weapon seems only to have been used in a few prototypes. There are unproven rumours that it was installed in some aircraft Lend-Leased to the USSR...

2. Oerlikon cannon

The relatively modest performance of the Oerlikon cannon has been generalized by many people to the inaccurate conclusion that all WWII 20mm cannon were slow-firing, low-velocity weapons. A good example is Ref. 37, in which R. Mikesh makes a valuable effort to analyze the Zero's armament, but simply ignores the fact that the Japanese Navy made a poor choice when it adopted the Type 99-1 and 99-2 Oerlikon derivatives. The locked-breech weapons that replaced the Oerlikon in most services had considerably superior performance.

3. B-17 losses

In early 1943, before the distasters of Schweinfurt and Regensburg, the book "The Air Offensive Against Germany" by Allan A. Hitchie (Henry Hall & Co, NY, 1943) was published. The author of this work was obviously influenced by the RAF, and he gave a very realistic assesment of the defensive firepower of the B-17s and B-24s, and its limitations. These defeats did not happen without prior warning.

4. Evolution

Ref. 35 gives the following statistic: In the last 6 months of 1942 only 40% of the hits recorded on B-17 bombers were cannon hits. In the autumn of 1943 this had risen to 80%. In 1944 there were 35% more cannon hits than machinegun hits.

5. Hispano Mk.V

The British reduced gun stoppages with the Hispano to 1 in 1500 rounds, and the deletion of the in-flight recocking device illustrates their confidence in the weapon. But in US service complaints about the reliability of the Hispano, especially its feed mechanism, were frequent. (e.g. "Great enthusiasm was expressed over the 20mm cannons in the SB2Cs, even though feed-mechanism discrepancies occur frequently." Ed Heinemann, by E. Heinemann and R. Rausa, Naval Institute Press, 1980.) The causes of this discrepancy are unclear. They may be related to maintenance problems or to the design of the gun mounts. American-made Hispano cannon were considered satisfactory by the RAF.

6. Serrate

Serrate was a homing device tuned to the emissions of the German Lichtenstein SN-2 radar. This allowed the Mosquito to operate against German nightfighters. There was a reluctance to allow radar-equipped Mosquitos to operate over Germany, because the highly advanced radars would almost inevitably fall into German hands.

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