Apparently the "crash dive" concept had not yet been thought of, as this would take considerable time to deploy and dismantle. This remained standard through the N class, commissioned 1917-1918. Experience in World War I showed that this was inadequate in the North Atlantic weather, and earlier submarines serving overseas in that war (E class through L class, including four of the K class) had their bridge structures augmented with a "chariot" shield on the front of the bridge. Starting with the N class, built with lessons learned from overseas experience, US submarines had bridges more suited to surfaced operations in rough weather.