Introduction
The Japanese Army and Navy have separate air forces each of which employs its own distinct types of bombs and fuzes. These ordnance items are dissimilar in construction and identification features, and each service utilizes its own system of designation.
For the most part the two types of bombs and fuzes may not be used interchangeably. Special adapters have been developed, however, which allow some flexibility of this rule. This has been particularly demonstrated in the use of Navy bombs by the Army in conducting antisubmarine warfare.
System of designation:
1. Type number - Items of ordnance, as well as most other items of military equipment, are given a type number indicating the year the article was finally adopted for service use. This may occur several years after the ordnance has been in production and actual use.
Until the reign of the present emperor, (Showa era; started in 1926) items were designated by the year of era. Now, however, the year of the Japanese Empire (Japanese year 2600 corresponds to our 1940) may be used. For items introduced up to the year 2600 the last two numbers are used in the designation. Thus type 99 means the item was adopted in 2599 or our 1939.
The year 2600 may be represented as type 100 or type 0, in a designation. The years 2601, 2602, etc., are usually represent by the last digit such as type 1, type 2, etc.
Experimental Ordnance items are assigned experimental type numbers indicating the year of the Showa era during which the experiment was authorized.
Ordnance items standardized in the eras preceding the Showa era; namely, Taisho 1912-1926 and Meiji 1867-1912, will be designated by the era and the year of the era. Type II (Taisho) = 1922, type 41 (Meiji) = 1908.
2. Mark number - Some ordnance such as Navy bombs developed for a special purpose will be designated by a mark number.
3. Description of ordnance - Some items may have a word or two following the type number which gives a brief description of the particular piece of ordnance.
4. Model - This term has several meanings but generally it indicates a change in basic design.
5. Modification - This is used to represent minor changes in design or a change in explosive filling.
Designation
Japanese Navy bombs are divided into classes: land bombs, ordinary bombs, special bombs, smoke bombs, practice bombs, target-marker bombs, training bombs, and dummy bombs.
"Land" bombs are bombs specially designed for use against land targets. They are usually of rough construction.
"Ordinary" bombs are designed for use against ships. They include both GP and SAP types. They are of smoother construction than land bombs.
Special bombs are designed for various special purposes and each special class is indicated by a mark number.
According to a captured document a new system of designating Navy bombs has been proposed. The existing bombs are not to be redesignated but new bombs will be assigned mark numbers as follows:
Marks 1 through 9, antishipping bombs.
Marks 10 through 19, chemically equipped bombs.
Marks 20 through 29, antiaircraft bombs.
Marks 30 through 39, antiland bombs.
As the name indicates practice bombs are used for practice bombing. Target-marker bombs are used as target marking beacons.
Dummy bombs are used for training and practice bombing. Training bombs are used for training in handling bombs.
Smoke bombs are used for concealment purposes.
Individual bombs in these main general classes are given further designations.
a. The type number discloses the year that the bomb was adopted for service use.
In the "land" and "ordinary" bomb classes, the first bomb of a given weight class is not assigned a type number but is merely indicated by the weight number. Subsequent designs of the same weight are assigned type numbers. Thus there is a No. 6 land use bomb and a type 97 No. 6 land use bomb.
b. The number indicates the weight of the bomb in units of tens of kilograms. Thus a No. 6 bomb weighs 60 kg., a No. 25 bomb weighs 250 kg, etc. This designation is as much an indication of size as it is of weight, No. 6 indicating a bomb of the 60 kg. size, and approximate weight.
c. A description of the bomb is indicated by the characters for land use, ordinary, etc. If it is a special bomb, the mark number is given.
d. Model: This term has several meanings but in this instance is used to distinguish different designs of bombs in the same general class.
e. Modification: This term represents a minor change in design or a change in filling.
Construction
There are two main patterns of construction of Navy bombs, typified by the "land" bombs and the "ordinary" bombs.
a. Land bombs: Land bombs arc of three piece construction. The nose is attached to the cylindrical body either by welding and riveting or by welding alone. The tail cone, which is filled with explosive is attached to the body by means of a collar or coupling ring. Either the body or tail cone is attached to the collar by welds and/or rivets and the final junction is made by attaching the other part to the collar by screws.
b. Ordinary bombs: Ordinary bombs are of two piece construction. The nose and body are manufactured of one piece, and are machined both inside and out. If the tail cone is filed it is threaded into the body or in the case of larger bombs an interrupted screw arrangement is used to attach it to the body. If the tail cone is empty a male base plate closes the after end of the body and the cone is attached to the base plate by threads or screws. The construction of special bombs and other general classes varies greatly and is covered in the description of each individual bomb.
Suspension
Bombs up to and including 250 kg. are suspended by a single U-shaped fixed lug. Two lugs 180° apart may be fitted to the bomb. Larger bombs may be suspended from a torpedo- release gear by two flat guide studs located 180° apart or by a suspension band fitted with the standard lug.
Fillings
Navy bombs are generally filled by casting the explosive directly into the case. The cavity is protected by a thick coat of lacquer. In some instances the explosive may be preformed into paper-wrapped sections which are usually additionally protected by a wax or a flannel coating.
Color and markings
During the war the Japanese Navy has modified the color system used to differentiate its bombs. Under both the new and old systems, the basic body color is grey; this color varies from greenish-grey to bluish-grey depending on variations in the paint and weathering conditions. This grey paint is applied over a red anticorrosive paint.
The old color pattern consisted of painting key colors as a broad band on the nose and tail struts. Usually these colors were the same. A band slightly aft of the suspension lug was an additional key. Thin red stripes 180° apart running from nose to apex of tail cone appeared on all service bombs.
In the new scheme all bombs containing explosive have the nose tipped in green. Key color bands appear aft of the green tip and an additional key color band may appear on the tail strut. The red stripes have been dropped. Colored body bands are used in some instances to indicate different modifications.
Size
The largest bombs recovered are 1,500 kg bombs.
Fuzing
As a rule Navy bombs of 250 kg. and larger in weight are fitted with fuze pockets in both nose and tail. The No. 6 and No. 3 sizes of land use and ordinary bombs have nose pockets only.
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