Chalk (military)

In military terminology, a chalk is a group of paratroopers or other soldiers that deploy from a single aircraft. A chalk often corresponds to a platoon-sized unit for air assault operations, or a company-minus-sized organization for airborne operations. For air transport operations, it can consist of up to a company-plus-sized unit. Oftentimes, a load of paratroopers in one aircraft, prepared for a drop, is also referred to as a stick.

The term was first coined in World War II for airborne troops during Operation Overlord, the Allied invasion of Europe. The aircraft flight number was placed on the troops' backs with chalk. It was later used during the Vietnam War, when it was common practice to number with chalk the sides of the helicopters involved in an operation. During the Battle of Mogadishu (1993), the battle plan called for four chalks from the 75th Ranger Regiment to fast rope down from hovering MH-60L Black Hawk helicopters around the target building. The rangers would then create a four-corner defensive perimeter. The plan failed as two of the Black Hawks were shot down, and the assault turned into a forced evacuation.

Chalk

Chalk /ˈtʃɔːk/ is a soft, white, porous sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO₃. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells (coccoliths) shed from micro-organisms called coccolithophores. Flint (a type of chert unique to chalk) is very common as bands parallel to the bedding or as nodules embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint).

Chalk as seen in Cretaceous deposits of Western Europe is unusual among sedimentary limestones in the thickness of the beds. Most cliffs of chalk have very few obvious bedding planes unlike most thick sequences of limestone such as the Carboniferous Limestone or the Jurassic oolitic limestones. This presumably indicates very stable conditions over tens of millions of years.

Chalk (disambiguation)

Chalk may refer to:

Surname

Chalk (TV series)

Chalk is a British television sitcom set in a comprehensive school named Galfast High. Two series, both written by Steven Moffat, were broadcast on BBC1 in 1997. Like Moffat's earlier sitcom Joking Apart, Chalk was produced by Andre Ptaszynski for Pola Jones.

The series focuses upon deputy headteacher Eric Slatt (David Bamber), permanently stressed over the chaos he creates both by himself and some of his eccentric staff. His wife Janet (Geraldine Fitzgerald) and new English teacher Suzy Travis (Nicola Walker) attempt to help him solve the problems.

Because of the very good reaction of the studio audience, a second series was commissioned before the first had been broadcast. However, journalists were critical of the show, highlighting stylistic similarities to Fawlty Towers. Some members of the teaching profession and its unions objected to the negative representation of teachers and the comprehensive system. The second series did not receive a stable broadcast slot, with many episodes aired after 10pm. The first series was released on DVD in December 2008.