The 9mm Parabellum was developed for the 
Luger autoloading pistol, which became the 
standard sidearm for both the German Army and 
Navy.  It's worldwide acceptance by militaries 
(including NATO) and law enforcement agencies is 
testimony to the 9mm's effectiveness as a field 
round.

    In 1955, when NATO adopted the 9mm as it's 
standard sidearm cartridge, the U.S.  kept the 
M1911A1 .45 Automatic pistol in service.  In 
significant part, the decision was made based on 
the fact that decades of .45 ammunitions and 
pistols had been stockpiled.

    To the dismay of Colt Auto fans, in 1985 the 
U.S. retired the M1911A1 .45 ACP and adopted the 
Berreta 92 in 9mm.  The debate as to the wisdom 
of this change seems to have momentum to carry it 
well into the next century.

    Being a smaller cartridge, an infantryman can 
carry more 9mm ammunition (or travel lighter).  
The handgun magazine alone, in the Berreta holds 
15, whereas the Colt tops at 7.  Each pistol may 
have an additional round in the chamber.

    Factory listings include a 115-gr. bullet 
exiting a 4" barrel at 1155 fps., with 340
ft-lbs. of energy.