German 15cm SiG 33 infantry gun. The heaviest weapon ever issued as an Infantry gun to any army during World War II. Its maximum range was 5140 yards and it was operated by a crew of 8.
Looking closer, it has the same carriage wheels as the 10.5cm Leichte Feldhaubitze (FH) 18/40, which would make it late production; the early production had spoke wheels without the rubber tires. For the early wheels, look at the US Army Infantry Museum's
Captured SiG 33.
