Rugged Island was to be the site for a war reserve magazine of rather unusual design, to consist of a forked tunnel driven into a cliff near the main access road. About 50 feet in, the tunnel would split into three passages, each about 30 feet long. At the fork, each of the passages would have a one foot concrete wall with a fire door separating it from the main tunnel, creating three sperate 300 square foot magazines at the end of a 50 foot access tunnel.
Had the project been completed, the magazines would have been used to store antiaircraft ammunition as well as both powder and projectiles for 6-inch Battery Const. #294. However, only about 30 feet of the main tunnel was excavated before work was halted in 1944.