Ok, here`s the official scoop on the shoulder patch from the Army Institute of Heraldry
The Institute of Heraldry Home Page
1st Engineer Brigade Insignia Page
Description: On a blue rectangular background with a rounded top, 3 1/8 inches (7.94 cm) in width and 3 1/4 inches (8.26 cm) in height, a modern anchor palewise behind a sub-machine gun fesswise on which is perched an eagle with wings displayed and inverted all in golden yellow.
Symbolism: The design was based on the design of the British Combined Operations patch which was worn by commandos, landing craft personnel, and others.
Background: The shoulder sleeve insignia was originally approved for the Engineer Amphibian Units on 17 June 1942. It was redesignated for all Army personnel assigned to the following amphibian units: Amphibian Tank Battalions; Amphibian Tractor Battalions; Engineer Amphibian Units; Joint Assault Signal Companies; Headquarters Ships Detachments (Type A); Headquarters Ships Detachment (Type B ); Headquarters Section (Army); and Amphibian Training Command - Pacific Fleet on 10 June 1944. The insignia was redesignated for the 1st Engineer Brigade and amended to update the description and add a symbolism on 20 July 2007. (TIOH Dwg. No. A-1-263)