Here's the nifty soft rubber-like plastic howitzer that was paired with the Auburn Jeep. After looking at this I wondered what piece of artillery this could have been modeled after and came to the conclusion that it most resembles the Rock Island Arsenal M101 105mm Medium Howitzer which entered production in 1941 (the M114 115mm Howitzer shares a similar outline but is twice the size).
The resemblance is close but remember the Auburn piece is just a toy and a caricature of any real artillery. The howitzer measures 3 3/4" (9.52cm) L x 1 3/4" (4.44cm) W x 1 5/8" (4.12cm) H. Enjoy! Opa Fritz and Oma Bettina