Prior to 1941, the Army and the Navy had their individual designs for and manufacture of all types of bombs, and each service had its own distinctive nomenclature to indicate a particular piece of ordnance. The Navy nomenclature was prefixed by the word "Mark"  (abbreviated Mk), the number of design was indicated by a Roman Numeral, and die sub-sequent modifications to the original design were indicated by the abbreviation "Mod" fol-lowed by the number of the particular modification; i.e., Mk XIII-Mod 2 500 lb. G.P. bomb. The Army nomenclature prior to July 1, 1925 was similar to the above, differing only in the method of designating the subsequent modifications of a particular design. A modification of an Army bomb was indicated by the abbreviation "M" followed by a Roman Numeral; i.e. Mk I - MII 100 lb. G.P. bomb.

In 1925, the Army changed its method of designation to avoid confusion with Naval ordnance; and since that time, the designation of all items has been prefixed by the ab-breviation "M" (for Model) followed by an Arabic Numeral. Subsequent modifications are indicated by adding the letter "A" followed by the number of the particular modification; i.e. M 38A2 indicates the second modification of the bomb originally adopted as the M 38.

Early in 1941, a joint committee for standardization of ordnance, known as the Army-Navy Standardization Board, was created and since its inception, bomb production, with very few exceptions, has been of the types approved by this Board for joint issue to the Army, the Navy, and the British forces. The responsibility of designing bombs for land targets was given to the Army, and bombs for Naval objectives or for carrier use were to be developed by the Navy. Designs accepted by this committee are indicated by the prefix "AN" followed by the Army or the Navy designation for the particular item. Thus, an Army bomb approved for joint production would be designated AN-M 64A1, and a Navy bomb which was accepted would be designated AN-Mk 33.

In this publication, the bombs have been categorized according to the particular ser-ies in which they were developed; hence, the section on bombs consists of four parts, each of which has an introduction listing the common characteristics of the bombs within that series. In brief, the four parts and the fundamental characteristics of each are as follows:

PART I:

U.S. ARMY "MODIFIED MARK" SERIES

Streamlined and filled with 100% TNT.

PART II:

U.S. ARMY "M" SERIES

Parallel sides, ogival nose, and boat tail; box type tail assembly construc-tion; and filled with 50/50 Amatol sea-led at both ends with TNT surrounds

PART III:

U.S. NAVY "MK" SERIES

Similar to design of Army bombs and filled with 100% TNT; discontinued with some exceptions under the stan-dardization program.

PART IV:

U.S. ARMY-NAVY "AN" SERIES

Similar to the "M" Series, excpet (a) third suspension lug added at center of gravity and 180° removed from other two lugs, and (b) base plate changed to the male type.

Since in the development of the "AN" series there have been two further modifications of the general purpose (G.P.) bombs within that series, successively the "AN-G.P." and the "AN-G.P.A1" modifications. The changes characteristic of these two modifications are dealt with the introduction to Part IV.