The aimable clusters are relatively new. They fit a 500 lb. bomb station and are desig-ned for precision bombing from high altitudes. To give the cluster the desired ballistic proper-ties, a standard box type tail assembly is attached by a single bolt to the aft plate of the cluster adapter. A strip of primacord (PETN) running full length along the side of the cluster serves to break the spring steel bands and allow the bombs to scatter when the serial burst nose fuze functions. The AN-M17A1 500 lb. aimable cluster is filled with 110 AN-M50A2 and AN-M50XA3 4-lb. incendiary bombs. The E6R2 cluster adapter (500-lb.), contains either AN-M69 or M74 incendiary bombs. The M23 500-lb. aimable cluster adapter contains 38 bombs of either the AN-M69, the M74, or the M77 incendiary and smoke bombs.

Where possible, the status of each bomb has been given according to Navy definition. "Service" indicates that the item is under current procurement. "Obsolescent" indicates that the bomb is becoming obsolete, that no future procurement is contemplated, but that large stocks may be on hand. "Obsolete" indicates that the present stock is almost exhausted and that it will not be replenished. Items of Army design not procured by the Navy are not classified as to status.

When under development, Army Bombs carry temporary designations which are later dropped when the bombs are standardized. Experimantal bombs controlled by the Army Ordnance Department are indicated by the letter "T"; modifications incorporated in the basic design carry the letter "E". Items in the developmental stage designed by the Che-mical Warfare Services, such as incendiary cluster adapters, are indicated by the letter "E" rather than "T", and subsequent revisions in "E" designs carry the letter "R".

If the developmental bomb is standardized for Army use the Ordnance Technical Comi-tee, the "T" or "E" designation is dropped and an "M" number assigned. When a modifica-tion on a standard item is under development, the change will be given an "E" or "R" de-signation; if the bomb thus modified is adopted as standard, it will take a designation in sequence in the "A" series, indicating an alteration in the basic design.

In undertaking the development of a new bomb, the Navy Bureau of Ordnance assigns a Mark number which will designate the bomb in the experimental stage as well as in ser-vice use. No system of "T" or "E" designations is employed. When adopted as standard by the Joint Aircraft Committes, the prefix "AN" is placed before the M or Mk designation.

An attempt has been made to differentiate between "clusters" and "cluster adapters" Property, the cluster adapter is merely the containing device or holder; when the adap-ter is loaded with bombs, the entire assembly becomes a cluster. In some cases the cluster adapter may closely resemble a bomb in construction (e.g. M23, M10A1), while in others the adapter is nothing more than a banding arrangements (e.g. M5).