Battle cry
During World War I in the Italian Front of 1915. Before battle, Italian soldiers would yell "Savoia" or "Avanti Savoia", which is "Come on Savoy!" or "Onwards Savoy!" in Italian (compare "For the king!" among British soldiers of the same era).

Modern: During World War II, Tennōheika Banzai (天皇陛下万歳, May the Emperor live for ten thousand years) served as a battle cry of sorts for Japanese soldiers, particularly in a "banzai charge". The most popular battle cry is "Ei ei oh" (エイエイオー), which is usually used at the start of battle.
"Avanti Savoia!" (English: Go Savoy!) was the patriotic battle cry of the Italian Royal Army during World War I and to a lesser extent, World War II. Infantrymen would scream this motto when launching an offensive attack, namely against the Austro-Hungarians.
During the Greco-Italian War (in WWII), the Greeks would shout "Αέρα!" (wind) as their battle cry.
During the Korean War, the Korean People's Army used the phrase "김일성 수령님 만세" (transliterated gim-ilseong sulyeongnim manse, translated as "Long live the Great Leader Kim Il Sung").
"Hooah" is the war cry of the United States Army, the United States Air Force, and the United States Space Force. "Oorah" is the war cry used by United States Marine Corps. "Hooyah" is the war cry of the United States Navy and the United States Coast Guard.
The Slavic version, "Ura!" (not to be mistaken with the "Hooah", noting in common) has been used by the Imperial Russian Army, the Red Army, Russian Ground Forces, alongside many more Eastern European armed forces. It was also used by Yugoslav Partisans as Juriš/Јуриш.
"Merdeka atau mati!" (English: Freedom or death!) Used by Indonesian national army and freedom fighters (Indonesian: Pedjoeang/pejuang) during the Indonesian National Revolution.
In Afghanistan, Norwegian troops of the Telemark Battalion would sometimes use the battle cry "Til Valhall!" (To Valhalla!) followed by Oorah.
Mujahideen and jihadists in the Middle East and North Africa shout "Allahu Akbar" (God is the Greatest).
During the Bangladesh Liberation War the Mukti Bahini would shout "Joy Bangla" ("Victory to Bengal" / "Long live Bengal") during their battles against the Pakistani military.
During the Indochina War in Vietnam, the Viet Minh soldiers usually used "Xung phong" (English: Charge) whenever attacking the enemy. The same battle cry would be used later by PAVN and NLF forces during the Vietnam War.
Each individual regiment of the Indian Army has a unique war cry. These chants are sonorous with the beliefs of individual castes and religions from which the troops belong to.
Croatian armed forces during the Croatian War of Independence would use "Za dom spremni". One would start by saying "Za dom!" and the rest would follow with "Spremni!". It translates loosely to "For home – ready!" or "For homeland – ready!".
Leeroy [sic] Jenkins is an internet meme, which has often served the purpose of an ironic or fatalistic parody of a battle cry, originating from a famous video of a World of Warcraft clan creating an intricate battle plan, before being party-wiped as a result of Leeroy Jenkins, who had been AFK at the time, charging in head-first. This gave rise to the phrase in first-person shooter games, where players will shout "LEEROOOOOOOOOOOOOOOOOY JEEEEEENKIIIIIIIIIINS!" as they charge at the enemy. The phrase has gained notoriety, making appearances in various non-World of Warcraft media.
Sangh Parivar and other Hindu nationalist organizations use the Hindu religious slogan Jai Shri Ram (Victory to Lord Rama) as a war cry during communal violence.
Various Kurdish groups such as PKK, YPG and Peshmerga use the following phrases "Bijî Kurdistan!" short for "Her Bijî Kurdistan" (English: Long Live Kurdistan), which is usually accompanied with "Her Bijî!" (English : Long live) "Yan Kurdistan Yan Neman" (English: Either Kurdistan or Extinction!)
During the 2022 Russian invasion of Ukraine, "Slava Ukraini" (Слава Україні! English: Glory to Ukraine!), often accompanied by a reply of "Heroiam Slava" (Героям слава! English: Glory to the heroes!), became an internationally-known battle cry not only among domestic forces, but also among Western, mostly NATO allies.

See also: 

References: Guilhem Pepin, ‘Les cris de guerre " Guyenne ! " et " Saint George ! ". L’expression d’une identité politique du duché d’Aquitaine anglo-gascon’, Le Moyen Age, cxii (2006) pp 263–281

External links: Philip Rance, 'War Cry' in The Encyclopedia of the Roman Army – Roman battle cries
Ross Cowan, The Clashing of Weapons and Silent Advances in Roman Battles – battle cries and the drumming of weapons in Roman warfare