Individual unit History for Army units is not kept very well, those you do find with good history is usually found in old Military Associations, and Books that for the most part now is out of print. I found the Gap in the 553d history I was looking for in a WWII book, by Shelby L. Stanton titled WWII order of battle 1984-1991 published by Presido Press in Novato, California, and a Private Lloyd May who served in the 553d in 1946, he lives at 1427 NW 7th Court, McMinnville Oregon, 97128. The following represents a corrected presentation of the History of one of the best, "THE 553d FIELD ARTILLERY BATTALION", and it is known that the primary weapon in WWII was 240mm Howitzer, and in later years, eight inch howitzers.

     Constituted 3 June 1916 in the Regular Army as the 2d Battalion, 18th Field Artillery
     Organized 1 June 1917 at Fort Bliss, Texas
     Assigned to the 3d Division, 12 November 1917
     Inactivated 15 February 1922 at Camp Pike, Arkansas
     Relieved from the 3d Division and assigned to the 9th Division, 24 March 1923
     Relieved from the 9th Division and assigned to the 6th Division, 15 August 1927
     Activated 15 September 1927 at Fort Des Moines Iowa concurrently 1st Bn, 9th
     Field Artillery consolidated with the 2d Battalion 18th Field Artillery
     Relieved from the 6th Division and assigned to the 3d Division, 1 January 1930
     Relieved from the 3d Division and assigned to the 2d Calvary Division, 23 Sep 1932
     Inactivated 1 December 1934 at Fort Riley, Kansas
     Activated I January 1935 at Fort Sill, Oklahoma
     Relieved from the 2d Calvary Division, 1 July 1940
     Reorganized and redesignated 1 March 1943 as 687th Field Artillery Battalion
     Activated 21 August 1944 Fort Bragg North Carolina
     23 March 1945 Departed to France, docked LeHarve France, located to Camp
     Lucky Strike France, then to Diipe France, Volkingen, Germany, Camp Washington
     France and Camp Pittsburg France, Major Keith M. Roberts was the first battalion
     commander, later promoted to Lt. Colonel. On 20 May 1945 the new commander
     appointed was Major Samuel M. Hart
     11 February 1946 were inactivated at Camp Kilmer New Jersey
     Redesignated 1 September 1948 as the 553d Field Artillery Battalion
     Activated 10 September 1948 at Fort Lewis, Washington
     Inactivated 15 December 1948 at Fort Lewis
     Activated 23 August 1950 at Fort Sill, Oklahoma
     On 15  May 1958 the 553d was removed from the Gyroscope list, (Gyroscope was when complete units stateside, replaced a complete unit overseas, the 553d went overseas as a Battalion and were to be replaced as a Battallion) on 25 June 1958 the 553d became the 3rd Bn 18th Field Artillery

The mission of 553rd at Fort Sill was to train artillery officers and men for duty on all present-day weapons at that time. The 553rd was equipped with 16-8inch Howitzers Split Trail, as well as 16 4.5inch Howitzers, which were the precursors to the 155mm Howitzer. The unit also was equipped with 16 105mm Howitzers.

The 4.5inch Howitzer was used for official firing shoots for training officers at the officer candidate school located on Fort Sill. This weapon was being phased out of the armyordinance and the ammunition were to be used up. For this purpose it was used almostextensively until 1953 when the 4.5 was completely dismantled. The artillery school began using 8inch and 105mm Howitzers for the training in 1954.
Under the Army Gyroscope Program the 553rd was ordered on January 19, 1956 to prepare for a unit transfer to Darmstadt, Germany by surface transportation. The advance party was to arrive by May 15, 1956 and the main body by July 12, 1956. Travel was accomplished aboard the USS General Alexander M. Patch. The unit at Darmstadt was the 18th Field Artillery Bn. The two units were changing duty stations under operation Gyroscope. The mission of the 553rd at Darmstadt was direct support of the 36th Artillery
Group, assigned under the command of the V-Corp. (Otherwise known as the Victory Corp.) and to maintain a constant state of combat readiness to protect the interest of NATO andthe 7th United States Army. In September of 1957 about 300 of the original men of the 553rd FA Bn. was replaced by a packet of that same amount from Ft. Sill.
I served in the 553d from 1953 thru its redesignation as the 3-18th and went Gyroscope with 553d from Fort Sill. The eight-inch towed weighed sixteen tons. We used to sing the old Tennessee Ernie Ford song "You load sixteen tons and what do you get, another day older and deeper in debt". We were a proud Battalion of Artillerymen, and always gave our best, with some great commanders, like Stanley Raub, Gustav Franke, Merle Ormond, Alexander Musick to mention some during my period of service with the 553d, all of the officers and enlisted men in the 553d were a proud group, I was, and always will have been, extremely proud to have known, and served with them. God Bless Our Deceased Members, and God Bless America.     ( There are no records of the 553d Field Artillery Battalion for World War I in the National Archives, 8601 Adelphi Rd, College Park, Maryland 20740-6001)
The 3d Bn 18th Arty went from Germany to Vietnam in1965, then to the Desert Storm conflict, and is at this writing located at Fort Sill Oklahoma.