Here's a nice cacheted cover for the U.S. Navy ship U.S.S. Isle Royale. As far as I know, it doesn't commemorate any specific event.
Postmarked: HC - USS ISLE ROYALE (AD-29) - December 5, 1967
Cachet: Purple rubber-stamped cachet featuring an aircraft carrier with planes taking off and landing. Text reads: "UNITED STATES NAVY / POWER AT SEA / for / HOMELAND PROTECTION".
Condition: Clean and neatly label addressed, with a couple of mild creases along the left edge. (Please see scan.)
MULTIPLE ITEM SHIPPING DISCOUNT: I will ship up to 4 covers for the single base shipping charge shown. For purchases of more than 4 covers, the shipping charge will increase by just a small increment for every 4 additional covers.