Complex sentence: The M1895 proved to be a significant advance in firepower for the Marines, while Army forces in the campaign were still burdened with heavy, manually-operated Gatling guns that required heavy artillery carriages pulled by mule transport.
Split into simpler sentences: The M1895 proved to be a significant advance in firepower for the Marines. Army regular forces in the campaign were still burdened with heavy, manually-operated Gatling guns that required heavy artillery carriages pulled by mule transport.