The M777 is a towed 155 mm ultralight howitzer (39‑caliber) that delivers heavier, longer‑range fires and is used for medium artillery support; the M119 is a towed 105 mm lightweight howitzer used by light/airmobile units for shorter‑range fires. Key differences: caliber (155 mm vs 105 mm), range and explosive power (M777 fires heavier rounds farther), and weight/mobility tradeoffs (M119 is lighter and more suited to airmobile operations while the M777 uses titanium to reduce weight for a 155 mm system).