When I was in VN, we could carry just about anything. Machine gunners were authorized to carry 1911s, but most didn't. I was a Plt. leader, and guess I could have been issued one, but didn't want one. To tell the truth, the 1911s were held in low regard by troops of my era. There was a week of qualification in basic, but no one could shoot them well. We were trying to minimize weight in the field, so they became an afterthought.
I found a 1911 along a dirt road, covered with fine sand, cleaned it and carried it in my pack in condition 3. I also carried, for a while, a sawed off Ithaca, sawed off at the pistol grip and just ahead of the mag. It was also in my pack, but not at the same time as the 1911.
The only company grade officer I saw carrying a pistol was the CC of A company, who carried a Browning HP as his only weapon.