I've attacked one, but not "successfully." Ran into a pretty small one, off the coast of Portugal (that seems to be a good place for me to find large groupd that'll blow me up) 3 river escorts, 2 V&W's, a Clemson, and a Bogue. Sank everything but the Clemson before it rammed me and broke me in two.
IXC in early '43,
-Qairyl