In the
United States Navy, aircraft carrier operations began with
USS Langley (CV-1) in 1922, and it served as a platform to experiment and develop
aircraft launch and recovery procedures. The first pilots had no signaling system for assistance from shipboard personnel.
Hand-operated signals prior to adopting paddles for better visibility at greater distance. The basic semaphore signal letters F for fast, N for low, U for high, and R for roger (or "right on") were retained with a few more specialized signals; but the original S for slow was replaced as shown in this illustration of the thirteen standardized LSO signals used by the U.S. Navy during
World War II. From the 1920s into the 1950s, U.S. Navy and Royal Navy LSOs used a variety of signals to assist pilots landing aboard aircraft carriers. The signals provided information on lineup with the deck, height relative to proper
glide slope,
angle of attack (fast or slow), and whether the plane's
tailhook and wheels were down. The final signal was "the cut" (a slashing motion at the throat) ordering the pilot to reduce power and land the aircraft. In a properly executed landing, the aircraft's tailhook snagged an
arresting wire that brought the plane to a halt. A "waveoff" was a mandatory order to abort the landing and go around for another attempt. Sometimes a proper approach drew a waveoff if the deck was "fouled" with aircraft or personnel in the landing area. LSOs faced the 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, the LSOs are free to lower the pickle. ==USN / USMC LSO qualifications==