Above the SPS, and directly behind the armour belt, was a series of compartments, typically used for washrooms or storage spaces, which were designed to allow for upward venting of overpressure from a torpedo hit. This scheme was designed to protect against a 1000 lb warhead, and had been tested and found effective in full-scale trials. The SPS was also a key component of the ship's damage control system, as lists resulting from flooding could be corrected by counterflooding empty void spaces, and/or draining normally liquid filled compartments. In the case of the loss of the "Prince of Wales" these spaces were used for counterflooding to reduce list.