He 111P - upgraded to Daimler-Benz DB 601 engines.
He 111H - more widely produced during World War II. DB 601 engines were changed to Junkers Jumo 211 engines. When the Jumo was fitted to the P model it became He 111 H.
He 111 H-16 - Fitted with Jumo 211 F-2 engines and increased defensive armament of MG 131 machine guns, twin MG 81Zs, and an MG FF cannon. (Late 1942)