This is from Drug War Crimes: The Consequences of Prohibition

I am pretty sure the author means that 19% of the 35% that tried it became addicted. Since I don't know the exact numbers lets say there were 10,000 soldiers and 35% of them tried herion. Thus 3,500 of them tried heroin, and of that 19% got addicted or 665 of the 10,000. Check my math if you want:
10000 * .35 = 3500
3500 * .19 = 665