An acoustic "hammer box" aboard a U.S. Navy minesweeper, circa in 1962. The device was used to detonate acoustic mines.
USN
<a rel="nofollow" class="external text" href="http://www.navy.mil/ah_online/department_arch.html">U.S. Navy All Hands magazine</a> <a rel="nofollow" class="external text" href="http://www.navy.mil/ah_online/archpdf/ah196210.pdf">October 1962</a>, p. 20.