Barracks at Town Hall 16: max level 18. At Town Hall 18 the cap is level 19. Max level per Town Hall: TH3 5, TH4 6, TH5 7, TH6 8, TH7 9, TH8 10, TH9 11, TH10 12, TH11 13, TH12 14, TH13 15, TH14 16, TH15 17, TH16 18, TH17 19, TH18 19.
Tap a Town Hall to open this item there. Dashed: not available at that Town Hall yet.