How did the instructor “build a swimmer” out of Douglas?

The instructor gave him proper training for swimming. He had put a belt around Douglas .The rope attached to the belt went through went through a pulley that ran on an overhead cable. He held on to the belt and made Douglas practice for hours, every day. Sometimes, the instructor relaxed his hold on the rope, the terror of drowning would seize Douglas. It took him months to overcome the fear of water. The instructor taught him to put his face under water and exhale and to raise his nose to inhale. It helped him shed the panic that gripped him under water.