The locomotive chimney would also be fitted with a spark arrestor. He obtained patents for a spark arrestor and a gauge glass protector. Some chimneys have a spark arrestor incorporated into the crown or cap. Takeoff and landing are from a simulated aircraft carrier deck, with arrestor wires. A gas-filled tube can also be used as a shunt, particularly in a lightning arrestor. As with the arrestor, a screen was incorporated to retain any large embers. A flush arrestor hook was fitted directly ahead of the tail wheel. Early carriers had a very large number of arrestor cables or "wires". R-1820 nine cylinder radial engines, a yoke type arrestor hook and a crew of four. This is followed by the carrier deck landing, attempting to snag the arrestor wire. The Sea Balliol T.21 had folding wings and arrestor hook for deck landings. To prevent such a situation a flashback arrestor is usually employed. For that reason a flashback arrestor is needed. Aircraft from the later production batch were fitted with arrestor hooks. Her arrestor cables were not upgraded at this stage, however.