Here's the quick easy and probably somewhat innacurate synopsis. The No 1 Mk 3 was developed for WW1 and was used during WW2 as well, some being refurbed, and the australians continuing to manufacture them. The No 4 line came into being sometime around WW2, and was used in later years as well. The No 5 is the one referred to as the Jungle Carbine, it was lightened and shortened for fighting in the far east and Asiatic conflicts. I personally have never heard of or noticed any references to No2's or 3's. I realise I havent provided much good info, but for piccies search wikipedia, it's fast and you'll see what they look like.