Hi,
I believe that the UK's Mark IX tank from WWI may have been considered the first Armoured Personnel Carrier, but I'm not sure that they were ever used in battle. And supposedly, the German Cold-War era Schützenpanzer Lang HS.30 is considered by some to be the first real Infantry Fighting Vehicle.
For information on the Mark IX you might want to look at "The British Tanks 1915-1919" by David Fletcher. I amnot sure of a good source document for the Schützenpanzer Lang HS.30, though.
Pat
Mark IX tank - Wikipedia
Infantry fighting vehicle - Wikipedia
Schützenpanzer Lang HS.30 - Wikipedia
PFJN got a reaction from TheSpecialist in History of IFV?