This battalion was activated on 15 November 1942 at Fort Sheridan, Illinois, as the third battalion of the 510th Coast Artillery (CA) Regiment. Major John B. Terrill, Jr. was assigned as commanding officer, with Captain True as battalion executive officer. Upon activation, the battalion was furnished with a cadre from the 506th CA Regiment, and a few weeks later its first fillers were received from personnel inducted at Ft. Sheridan. Major Terrill was promoted to Lieutenant Colonel on 12 December 1942.
The period from 15 November 1942 to 20 January 1943 was spent largely in the training of cadre and the formation of the instruction teams among the battalion’s officers and noncommissioned officers, which were to conduct basic training when the battalion’s fillers were received. On 20 January 1943, the unit was re-designated the 225th CA SL Bn (AA). Lt. Col. Terrill left the battalion to assume the duties of executive of the 112th AAA Group, and Lt. Col. F. T. Ostenburg assumed command of the battalion, with Major Wallace H. DuShane as battalion executive. On 23 and 24 January, the battalion received a large number of fillers, bringing it almost up to its TO strength. The fillers were drawn about equally from New York and from the area of Kentucky, Ohio, and Tennessee, one group coming from Camp Upton, New York, and the other from Fort Knox, Kentucky.
With the arrival of its fillers, the battalion began an intensive schedule of basic training. The training in basic subjects proceeded efficiently and with gratifying results, but during the entire period of the unit’s stay at Ft. Sheridan, the problem of satisfactory training in the use of its basic weapon was unsolved, due to the inability to obtain sufficient night target missions. Unfavorable weather conditions, combined with smoke and fog – common to the Chicago area – grounded target planes night after night, and it was only on extremely rare occasions that the unit had an opportunity to practice tracking.
