Training Rooks III is the last training upgrade, making your Rooks level 9 for late-game gang wars. At £20,000 it is one of the costliest Ringleader purchases.
Training Rooks III is entry 5 of 17 in the Ringleader branch, one of the three branches (Ringleader, Insider and Swindler) on the Rooks' 39-upgrade board. It is bought with money and materials, not skill points: £20,000, 100 Metal, 50 Silk. Before Training Rooks III unlocks you need Training Rooks II and Enhanced Firepower.