This class consisted of 75 wagons converted from the standard, N.Z.R. type , single bolster wagon in 1920-2. Unlike the longer M class wagons they could only carry two wooden coal boxes. From the mid twenties they began to be replaced by other types and had gone by 1936.         Right: IM722 blown up from a 1920's photograph of North Fremantle

1920	585, 587, 593, 596, 598, 610, 628, 644, 674, 701, 703, 706, 707, 720, 722, 761, 766, 769, 775, 784, 794 from I
1921	589, 591, 595, 600, 606, 613, 615, 620, 623, 625, 627, 632, 635, 640, 645, 646, 648, 653, 654, 655, 657, 665, 668, 672, 699, 715, 721, 723, 725, 726, 730, 731, 733, 734, 740, 742, 746, 749, 751, 755, 759, 762, 765, 767, 768, 770, 776, 782, 783, 786, 787, 789, 792 from I
1922	597 from I
1926	591, 595, 606, 615, 625, 635, 640, 645, 648, 653, 654, 665, 703, 723, 731, 765, 766, 787, 792, 794 replaced by GC
1928	628 replaced by GC
1929	746 to I 593, 600, 722, 786 to JETTY 357, 359, 361, 360 respectively 589, 769 replaced by M 627, 657, 783, 789 replaced by MA 587, 623, 646, 730, 734 written off
1931	610, 699, 715, 721, 751 to I
1934	742, 767 to I
1935	585, 596, 598, 613, 620, 632, 644, 655, 668, 672, 674, 701, 706, 707, 720, 725, 726, 733, 740, 749, 755, 759, 761, 762, 768, 775, 776, 782, 784 written off. 770 to JETTY 298

At least two of the IM converted to JETTY wagons (ex 593 and 770) were reconverted to class I in the 1942 - 1944 period.