There was no such ship class as far as I can tell. In fact, reading about AE's in Wikipedia, I found a number of entries that talked about ammunition ships carrying reloads of mines.
On 17 October she departed San Francisco for Alaskan waters where she issued a load of mines to smaller ships to be planted as a defense for the base at Adak. - Wikipedia entry on USS Pyro (AE-1)
Is there some playability issue that required the creation of MLE's?
AE's... Well, if I didn't enjoy spending the time to use every little resource, I would never use them. Historically, it appears to be quite correct that underway replenishment of ammunition did not occur until very late in the war.
The highlights of Shasta's wartime career came in 1945. In February, she participated in the first successful underway replenishment of ammunition. Later, while re-supplying the warships supporting the assault on Iwo Jima, she came under the fire of Japanese shore batteries. Her most harrowing experience occurred on 5 June when she was battered by the force fourteen winds of a typhoon off the southeastern coast of Okinawa. Though her cargo had shifted and much of it had been damaged, Shasta still managed a successful rearming rendezvous before sailing for Leyte Gulf in the Philippines.- Wikipedia entry on USS Shast(AE-2)
