This old general's battle record is stellar — his war service was distinguished.
Tips
history
From 《韩非子·五蠹》: 弃私家之事，而必汗马之劳 — Han Feizi argued that soldiers give up family life to sweat with their horses on campaign. 汗马 originally meant 'warhorse lathered with sweat', the symbol of hard military service.
usage
The military origin lingers in the tone — the phrase is reserved for serious, sustained contributions to an enterprise, not small favors. Typical frame: 为 [org/cause] 立下汗马功劳. Contrast with 举手之劳 (a trivial effort).
