marching order; order to advance; go-ahead
Primarily a military term for an order to move forward or attack. Figuratively, it can mean a signal or permission to proceed with a plan.
The commander gave the troops the order to advance.
The president gave the go-ahead for the new project.
出撃命令 specifically means an order to sortie or launch an attack, while 進撃命令 is a broader order to advance or move forward.
ゴーサイン is a common loanword for 'go-ahead' in non-military contexts, whereas 進撃命令 retains a military flavor even when used figuratively.
Compound of 進撃 (advance, attack) and 命令 (order, command).