For the first two years of the war Rennie continued as an instructor, as the instructing staff could not be spared for active service. During this time he helped select the initial officers and
Non-commissioned officers for the
28th (Maori) Battalion, and was for a period 'in
interregnum' the
Regimental Sergeant Major of Army Schools. Rennie observed that he, "must have been the youngest to have done so and, I am sure, with the most curious assortment of ranks—I was a substantive lance-corporal, temporary sergeant, acting warrant officer first class." He also took part in the seizure of the island the following month. When the
3rd Division was disbanded later in 1944, Rennie joined
2nd Division in
Italy, arriving early in 1945. He was posted to 23rd Battalion and commanded a
Vickers MG platoon, seeing action in the river-crossing the 2nd Division conducted as it pushed northwards through Italy in the final months of the war in Europe. His unit finished the war near
Trieste, and was involved in the stand-off with
Yugoslav Partisans. ==Jayforce to NZSAS==