Time of Test Firing

Routine test firing of VT fuzed ammunition by all ships shall be conducted quarterly or as nearly so as the opportunity offers. Each ship shall perform the routine test quarterly on all lots of VT fuzes (except obsolete models) of which there are 250 fuzes or more on board. This firing shall be in addition to target-practice allowances. The purpose of this routine test is to provide the Bureau with sufficient information about the functioning of these fuzes with the least expenditure of ammunition. Careful attention to the form and completeness of reports is therefore required.

Exhange of Ammunition

In contrast to the wartime practice, authorization to individual ships for the exchange of their VT fuzed ammunition on the basis of individual test firing is now rescinded.

The peacetime policy of the Bureau of Ordnance, now in effect, is to complie and ana-lyse all test-firing reports and issue blanket recall and unserviceability orders upon the basis of these over-all results and upon the basis of other important considerations such as availabilty and distribution of replacements, availability of rework personnel, existence of improved type fuzes, etc. Replacement authorization will also be issued to individual ships or units in exceptional cases upon requests by the ship of unit commander or by higher fleet commands.

Detailed Instructions

Detailed instructions for the conduct of quarterly tests are as follows:

The routine test consists of firing over water of from 6 to 40 rounds, depending upon performance results, from each lot of ammunition containing 250 or more VT fuzes. The test rounds shall be taken from regular stowage and shall not be rounds held in ready service lockers. When practicable, the stabilized gun elevation shall be 15° for tests in five-inch and six-inch guns, 10° for those in three-inch guns, and 30° for those five-inch rocket launchers. Other conditions of test are left to the discretion of the ship, but ge-neral information concerning these conditions is requested in paragraph 1 of the test re-port form (NAVORD FORM 1758). The test report form is shown in Figure 15. Detailed test results are requested in paragraph 2 of the report form. In paragraph 2, columns 5 and 6 of the test results table indicate the round at which the test shall be stopped. The met-hod is to compare the number of normal rounds observed previously in the test (column 5) with reference numbers (column 6) as given in the table. This test procedure saves ammunition by stopping each test when sufficient information has been obtained about the lot. A few rounds will give adequate information if the lot under test is very good or very bad, but more are required if it is close to the limit of acceptable quality.

Figure 15. Test Report Form-NAVORD Form 1758

General Information

General information requested on the form is as follows:

VT Fuzes Tested. Fill in Mark, Mod, Lot No., and total number of this lot aboard after completion of test

Date of Test. Give day, month and year.

Average Stowage Temperature During Month Before Test. Fill in average high and average low temperatures, during past month, of compartment in which lot was stowed.

Temperature of Porjectiles When Fired. Give best estimate of the actual temperature of the projectile or rocket just prior to loading in gun for firing.

Date VT Fuzes Removed from Cans (if canned). VT fuzes will be issued in cans in the near future. Fuzes unsealed for the same length of time shall be used in the test of the lot, if practicable.

Gun. Fill in caliber, mark and mod, and ESR (or caliber, mark, and mod of rocket laun-cher).

Area of Operation During Month Before Test. Give general area; for example, North Atlantic or South Pacific.

Weather Conditions. State weather rainy, cloudy, or clear.

Air Temperature. Give average surface temperature during test in degrees Fahrenheit.

Wave Height (in feet). Estimate height of waves in feet.

Date of Last VT Fuze Report. Give date of last previous VT fuze routine test report on any VT fuze lot.

Detailed Test Results

Under the detailed test results (paragraph 2) record the type of fuze action observed on each round, stop watch time to burst in seconds, the observed height of burst above the water in feet, and other significant data.

Type of Fuze Action. Fuze Action is classified into three general types, as follows:

NORMAL. A burst which occurs upon approach to the water at the end of flight is a "normal", recorded as "N". With all modern-types of Naval VT fuzes, these bursts will occur at heights above the water from a few feet to 200 feet. Average normal heights for A.A. fuzes incorporating the wave-suppression feature (Mks 53, 58, 59, etc.) are 15-20 feet. However, record "N" any burst under 200 feet.

PREMATURE. A burst which occurs along the trajectory not near the end of flight is a "premature", recorded as "P". Burst near the end of flight but above 200 feet are to be reported as prematures.

DUD. A burst which occurs on impact with the water is a "dud-impact burst", recorded as DIB. A round that enters the water without any explosive action is a "dud-splash" re-corded as DS. Either of these is considered dud action so far as the VT fuze is concer-ned.

No Observation. "NO" shall designate a round in which the type of fuze action is not ob-served. This in effect designated the round as non-normal in fuze performance.

Distinction Between Low Normals and Duds. The operating radius or sensitivity of WSF (Wave-Suppression Feature) fuzes is automatically adjusted to a smaller value along low trajectories and upon approach to the sea. This latter fact has in the past caused some confusion in identifying normal operation in routine tests in which typical height of WSF fuze operation is 20 feet. A low normal burst can be distinguished from a dud-impact burst, however, by the appearance of the flash above the water and by a large "mushroom" of black smoke which  appears just above the water; and at the same time fragments can usually be seen striking the surface over an area of forty or fifty feet in diameter. This easily observed by the control officer or other persons located suffici-ently high in the ship, and by using binoculars. A dud-impact burst, DIB, produces a ver-tical colums of water and spray and a thin wisp of smoke, which usually blows away rea-dily and disappears. Little or no fragmentation is noted in this case. Complete duds, DS, make only a small splash. Most duds occuring in routine firing tests of VT fuzes are of this splash type, as no VT fuzed projectiles thus far issued contain base detonating fu-tes.

An estimate of the height of the normal bursts by any practical means is desired. A sex-tant, stadimeter, or mil scale in binoculars is suggested to assist visual estimates. Close attention to distinguish low normal bursts from impact bursts is important.

Use of Table to Determine Round at Which to Stop Test. Columns 5 and 6 are provi-ded in the table to determine the round which to stop the test. In column 5 the number of normals previously observed in the test are added together to provide a running cu-mulative total. Thus, if the following type action is observed from a series of rounds: N, DIB, N, N, P, P, N; the record in column 5 is, 1, 1, 2, 3, 3, 3, 4. The 4 indicates that there were four normals at the end of seven rounds. This number is then compared with the reference numbers given in column 6a and 6b (for this number of rounds) to decide when to stop the test. If the number in column 5 is equal to or less than the number in column 6a, or equal to or greater than the number in column 6b, stop the test. If the number in colums 5 lies between the reference numbers in column 6, keep testing. The test will certainly stop at the end of 40 rounds. In the example givem, the cumulative total in column 5 was 4 at the end of seven rounds, and the reference numbers for se-ven rounds are 0 and 7. Therefore the test was continued. Other examples of the use of column 2, 5, and 6 are as follows:

Example 1

Col. 1

Col. 2

Col. 5

Col. 6

Round
Number

Type of Action
Normal N
Premature P
Dud-spash DS
Dud-Impact Burst
DIB
No Observation No

Cumulative
number of
Normals in
this
number of
rounds

Contiume test if number in Col. 5 lies between these
numbers 6a (exclusive) 6b

1

N

1

x

keep testing

2

N

2

x

"

3

N

3

x

"

4

DS

3

x

"

5

N

4

x

"

6

N

5

6

"

7

P

5

7

"

8

N

6

7

"

9

P

6

8

"

10

N

7

8

"

11

N

8

9

"

12

M

9

9

stop test (since Col. 5 equals 6b).

Example 2

Col. 1

Col. 2

Col. 5

Col. 6

Round
Number

Type of Action
Normal N
Premature P
Dud-spash DS
Dud-Impact Burst
DIB
No Observation No

Cumulative
number of
Normals in
this
number of
rounds

Contiume test if number in Col. 5 lies between these
numbers 6a (exclusive) 6b

1

P

0

x

keep testing

2

DIB

0

x

"

3

N

1

x

"

4

N

2

x

"

5

N

3

x

"

6

DS

3

6

"

7

NO

3

7

"

8

N

4

7

"

9

P

4

8

"

10

DS

4

8

"

11

P

4

9

"

12

DIB

4

9

"

13

N

5

3

10

"

14

DS

5

3

10

"

15

P

5

4

11

"

16

DS

5

4

11

"

17

N

6

5

12

"

18

DIB

6

5

12

"

19

P

6

6

13

stop test (since Col. 5 equals 6b).

Instructions in Mailing Report

Upon completion of test firing, the completed test report from should be fowareded by RESTRICTED air mail to the Chief of the Bureau of Ordnance, with copies to appropriate commands.