The term 'massive casualties' is correct and can be used in written English.
You can use the term to describe a large amount of people or things that have been injured or killed as a result of something, usually a battle or an incident. For example: The fierce battle resulted in massive casualties on both sides.
His forces suffered massive casualties, many times the toll inflicted on the French.
The massive casualties occurred even though the government had evacuated nearly 800,000 people ahead of the typhoon.
The efforts of Sir Robert Jones and the massive casualties of World War I led to the founding of many orthopedic training centres in the early 20th century.
History teaches that Americans are prepared to accept and inflict massive casualties in pursuit of victory (witness the campaign against Japan in the second world war).
Susanna John, whose home adjoins the evacuated building, said she had heard tales from outsiders claiming to have seen the crash, and accounts of massive casualties and mayhem.
The decision to drop the bomb was founded on the conviction that a blockade and invasion of Japan would cause massive casualties.
Soon the group spread out in a tactical patrolling formation, making it less likely that an ambush would result in a "mass cal" or massive casualty situation.
Mr Maliki admits that he has blocked a big offensive in Sadr City, the crowded east Baghdad slum which is the militia's main support base, for fear of massive civilian casualties.
Phoney stories exaggerating the strength of Iraqi forces in Kuwait, the likelihood of massive coalition casualties and of an invasion of Saudi Arabia, and telling of the 'murdered' incubator babies in Kuwait City, were transmitted without demur.
A National Intelligence Estimate on Iraq that was issued in January 2007 by the United States intelligence agencies also warned that the withdrawal of American troops over the ensuing 12 to 18 months would probably lead to "massive civilian casualties and forced population displacement".
(That is hardly a far-fetched scenario; a National Intelligence Estimate on Iraq issued in January 2007 by American intelligence agencies warned that the quick withdrawal of all American forces would probably lead to "massive civilian casualties and forced population displacement").
