In a message dated 4/3/99 2:08:53 AM Eastern Daylight Time, MercutioV@aol.com 
writes:

Maya(Lecture Mode): The N2 Mine is NOT a nuclear device. It is almost

 >> completely dissimilar. In fact, the term N2 actually stands for 
 �Non-Nuclear.�
 >> The N2�s are many things, but a nuclear weapon is not one of them.
 >>
 >  Biles:  So what IS it?
 
 Maya: Nobody knows. Hideaki and Sadamoto never saw fit to explain them
 to us beyond what N2 stands

The N2 is described in a blurb in the Viz translated version of Sadamoto's 
manga as being a tactical nuclear device.  It is certainly not in the 
television continuity.