Here is the little 37mm cannon.

Original pen and ink and wash sketch, signed by Reeks, of soldiers with 37mm cannons on shore, warships in the distance. Original pen and ink and wash sketch, signed by Reeks, of soldiers with 37mm cannons on shore, warships in the distance. Title from typed label affixed to verso. It continues: "This gun is dug in just a rock's throw from the enemy - trying to blast him from his hole. Every time it would fire, the enemy would spray it with machine gun fire. Warships do their job in the B.G. Weapons Co, 3 BN., 2BR., 5 Div., i 37 mm." Censor's stamp. Reeks joined the USMC in 1941 and saw action on Guadalcanal, New Georgia, Bougainville and Saipan. He was the only official combat artist to land on Iwo Jima with the invasion force and spent thirty days on the island sketching the campaign.