During the 1950s polio epidemic, stainless steel hydrotherapy tanks, known as Hubbard tanks, were used as a form of rehabilitation for children paralyzed by the disease. Touted to improve circulation and build muscle strength, the treatment involved immersing a patient in warm water up to their neck. The combination of the water jets, buoyancy, and heat helped them move weak or paralyzed limbs more easily and with less pain. As polio rates declined and new rehabilitation methods emerged, the use of hydrotherapy tanks gradually tapered off after the 1950s.