The Easter/April Fool's Day combination is a rare occurrence, but happened in 1945.
April 1, 1945 was also the day that US forces invaded Okinawa. I've heard that they were relatively surprised by the lack of Japanese resistance on the beaches. Of course this was part of Japanese military strategy - the resistance was inland and on the south of the island, and the battle ended up lasting over two months.
Was this strategy really a surprise to the US military?
Yes this strategy was a surprise to the US military, a complete surprise. American intelligence hadn't even guessed that the landing would be virtually unopposed.
"Dashing from his landing craft, anxious and ready to fire, one Marine saw an earlier arrival sunning himself and flipping through a comic book. American fear shifted to amazement and euphoria. . . . Other veterans of previous landings wondered where and when the Japanese would spring their trap: April 1 was April Fool's Day as well as Easter Sunday. Still others grinned and yelped at their barely believable luck. Relief spread from jubilant infantrymen on the beaches to skeptical communications and intelligence personnel still on the ships."
Tennozan by George Feifer, Chapter 10