海,陸,空

陸軍 Land forces; 海軍 Navy; 空軍 Air force

陸軍 Land forces
陆军是人类历史上最古老的兵种，主要在陆地上作战。冷兵器时代主要兵器有刀、剑、弓、矛等，現代的陸軍兵器則包括槍械、火炮、戰車、直昇機、飛彈等，多不勝數。现代陆军已经有多个兵科，如步兵，裝甲兵，炮兵，陆军航空兵，工兵等。目前是世界上人数最多的兵种。
Army (From Latin armata ("act of arming") via Old French armée) can, in some countries, refer to any armed force. More commonly, however, it is only used specifically to refer to a land force of the military. Within a national army, an army can also refer to a large formation, usually comprising one or more corps.
海軍 Navy
海军古称水军即一国在海或湖泊河流上执行作战任务的部队。包括海军航空兵、海军水面舰艇部队、海军潜艇部队、海军陆战队、海军基地警备部队以及其它特种部队。其一方面的作用为保卫该国海上疆域、维护该国海上权益，另一方面为将该国的军事、政治力量延伸到海洋及海洋周边的陆地。
A navy is the branch of a country's military forces principally designated for naval warfare and amphibious warfare (marines) namely lake or ocean borne combat operations and related functions. It includes operations conducted by surface ships, amphibious ships, submarines, and seaborne aviation, as well as ancillary support, communications, training, and other fields; recent developments have included space related operations. The strategic offensive role of a Navy is projection of force into areas beyond a country's shores (for example, to protect sea-lanes, ferry troops, or attack other navies, ports, or shore installations). The strategic defensive purpose of a Navy is to frustrate sea-borne projection-of-force by enemies. The strategic task of the navy also may incorporate nuclear deterrence by use of nuclear missiles.
空軍 Air force
空軍是現代化三軍當中成立最晚的一支，許多國家直到第二次世界大戰結束之後才有獨立的空軍出現。空軍的任務在於利用飛機與其他在空中飛行的武器系統進行武力投射，保護我方空域的充分使用，壓製作戰另外一方對於我方空域的干擾與使用他們自己的空域，支援其他軍種達到戰術與戰略目標的執行。 許多國家的編制上，空軍必須支援陸軍作戰的需求，包括對地面目標的攻擊，空運，空投以及其他相關的任務。即使這些國家的陸軍擁有自己的飛機，通常在任務或者是飛機的型態上與空軍是有所區別。有些國家的空軍同時也指揮彈道飛彈與防空飛彈兵力與系統。也有的國家在空軍的編制內有進行陸上作戰的特種部隊或者是空降部隊。
An Air force is a military or armed service that primarily conducts aerial warfare. It typically consists of a combination of fighters, bombers, helicopters, transport planes and other aircraft. Many air forces are also responsible for operations of military space, intercontinental ballistic missiles (ICBM), and communications equipment. Some air forces may command and control other air-defense assets such as antiaircraft artillery, surface-to-air missiles, or anti-ballistic missile warning networks and defensive systems.

if you talk about the soldiers in the army force ... thay will be navy, air, army

海(Sea) 陸(Land) 空(Sky)
軍事上:海軍(navy) 陸軍(army) 空軍(air force)

海 = sea, ocean
陸 = land, ground
空 = air

Sea,Land,Sky

sea, land, sky