The M422A run of jackets started in the 1941 fiscal year and were replaced by the AN6552 in 1944. There is variation between M422A contracts, such a length of the windflap and length of the sleeves relative to the body. There were 8 AN6552 contracts, by Block, Bogen and Tenenbaum, American Sportswear, Willis and Geiger and Monarch and again slight differences between each. All this makes any generalised comparison difficult, but M422As had USN painted behind the collar in yellow, black or silver whilst on AN6552 jackets they only had US as they were issued to the USAAF and the navy. In essence M422A and AN6552 naval jackets are remarkably similar. I have owned examples of both types.