In 1842, McCulloch went back to surveying and intermittent military service. At the Battle of Plum Creek, August 12, 1840, he served as a scout against the Comanches, and then commanded the right wing of the Texas army. When a Mexican raiding party under General Ráfael Vásquez invaded San Antonio in February 1842, McCulloch was prominent in the fighting that pushed the Mexicans back beyond the Rio Grande. A second Mexican raid led by General Adrian Woll in September of that year again captured San Antonio. McCulloch then served as a scout for Captain Hays' Rangers. He and his brother, Henry, subsequently took part in the failed Somervell expedition and both escaped very shortly before most of the Texans were captured at Ciudad Mier, Mexico in Tamaulipas, December 25, 1842.