incoming plane and held colored flags for visibility. Because LSOs waved colored paddles, flags, or wands, the officers became unofficially known as "Paddles" in the United States Navy, or "Batsmen" in the Royal Navy, while the trade was referring to as "waving". LSOs in different navies Both the U.S. Navy and Royal Navy employed LSOs. The main difference between American and British LSOs was the nature of their signals. Generally, U.S. Navy signals were advisory, such as indicating whether the plane was on glide slope, too high, or too low. On the other hand, Royal Navy signals were usually mandatory, such as ordering the pilot to add power, or come port. When "crossdecking" (pilots from one navy operating off a carrier of the other), the two navies had to decide whether to use the American or British system. Britain stopped using LSOs in the 1970s when the use of arresting gear and catapults was discontinued (and aircraft shifted to STOVL aircraft such as Harriers). In contrast, the Imperial Japanese Navy had no LSOs. Instead, its carriers employed a system of colored lights much like today's general aviation runway edge lights at most airports. However, each Japanese carrier assigned a sailor to wave a red flag in case a landing was to be aborted. Optical landing system From the late 1950s, carriers evolved from the original straight or axial-deck configuration into the angled flight deck, with an optical landing system (OLS) providing glide slope information to the pilot. As such, the system of using both the OLS and the LSO was developed. Together with the OLS, the LSO provides input to the pilot via a radio handset (that looks like a telephone handset), advising of power requirements, position relative to glide path and centerline. The LSO also holds a "pickle" (a handheld switch box) that controls a combination of lights attached to the OLS to indicate "go around" using the bright red, flashing wave off lights. Additional signals, such as "cleared to land", "add power", or "divert" can be signaled using an upper row of green lights called "cut lights", or a combination thereof. Often, pictures of LSOs show them holding the pickle switch over their head. This is done as a visual reminder to the LSOs that the deck is "fouled" – unsafe for an approach, with aircraft, debris, or personnel in the landing area. Once the deck becomes clear,