During the Korean War, a U.S. Marine Unit belatedly arrived in Korea and saw an Army troop getting ready to camp out on the roadside. A Marine officer advised the troop to climb up the mountainside by saying that the place had a high risk of being bombarded by the enemy. The commander of the troop ignored the advice and the troop eventually got bombed out.
The Marine Corps and the Army had different levels of experience and training. The U.S. Army was poorly trained and the officers lacked in field battle experience. The Army commander did not want to climb up the mountain because of insufficient energy. On the other hand, the Marine Corps still had most of the veterans of World War ll as promotion was slow there and marines were always ready to fight.
There is a saying in the Marine Corps: Once the country enters a war, the Marine Corps runs to the storage and takes out all the weapons they have. The list of weapons includes the ones abandoned or improperly taken care of by the Army during World War ll as well as the ones supplied to the marines. It is a tradition of the Marine Corps to collect all the weapons they can find and prepare for a future war.
This means weapons used by the Marine Corps are always more outdated than the ones owned by the Army or are secondhand weapons abandoned by the Army. The situation was pretty much the same during the Vietnam War. In the National Museum of the Marine Corps near Washington D.C., there is a photo of a marine descending from a helicopter during the Vietnam War. The helicopter in the photo is not the UH-1 used by the army at that time but is a secondhand Sikorsky. One marine in one of the photos is holding an M-14 rifle rather than an M-16.
Marines gave a self-mocking explanation as to why the Marine Corps uses outdated weapons: To use their anger in killing as much enemies as possible. Receiving a much smaller budget than the Army would be the real reason behind it but a philosophical explanation would be a warning against a huge dependence on state-of-the-art technologies and weapons.
Cutting edge weapons exist not to spare soldiers from the hardships and dangers but to help win a war. If a country and its military forget about this and only seek convenience and safety, they can put themselves at risk.