Top of the Line, in 1978 Deep Carry
Today there is no shortage of compact, sub-compact, and even micro-compact 9mm handguns that are designed to be small enough for pocket or ankle carry. However, in the early 1970s about the best you could get in that size, barring a manually-cycled Semmerling LM4, was a .25ACP mouse gun like a Colt Junior or Browning Baby or a J-frame/Dick Special.
Then came the OMC/AMT Back Up.
More in my column at Guns.com.