[narwan]

Light infantry has nothing to do with the amount of 'weight' a trooper carries into battle but refers to the TO&E and the organisation of the larger formation. Light formations have fewer heavy equipment and what they do have is often of a different kind. The 70mm howtizers you mentioned are a good example. They are much lighter than what one usually finds in a comparable infantry formation and can be carried in parts by mule. The example you gave that the japanese had some arty at Kokoda only illustrates why light infantry (the japanese) is sometimes better than regular (or heavy) infantry (the Australian CMF troops); their lighter equipment can go where the heavier equipment of the normal formations can't (or not in time at least).