A Howitzer usually has a shorter barrel than a Gun, and has a higher angle of trajectory. This enables the Howitzer to drop it's shells onto a target from a high angle. This indirect fire enabled Howitzers to fire on targets hidden behind natural or man-made obstacles, and were better able to deal with fortifications, making them extremely important during the First World War.
4.5 inch Howitzer
6 inch 30 cwt Howitzer
6 inch 26 cwt Howitzer
8 inch Howitzer Mk I-V
8 inch Howitzer V-VII
9.2 inch Howitzer
12 inch Howitzer
15 inch Howitzer