OP 1664 - U.S. Explosive Ordnance (Vol. 2); Part 7 - Guided Missiles and Fuzes; Chapter 22 - Guided Missile Fuzes and Detructors; Section 1 - Fuzes: T715 and T84 Series (Athwarpship Mechanical Impact)

U.S. EXPLOSIVE ORDNANCE

PART 7 - GUIDED MISSILES AND FUZES

Chapter 21 - MISSILES

Section 1 - FUZES

T715 and T84 Series (Athwarpship Mechanical Impact)

Missiles	JB-2 or "Loon"
Functioning	All-ways action, long-delay arming
Arming data	T715 can be set 4 to 45 miles T84E1 - 4 to 5 miles T84E2 - 12 to 15 miles T84E3 - 25 to 30 miles T84E4 - 40 to 50 miles

General: These are the mechanical fuzes of American design or the JB-2 or "Loon" missile. The T84 series was replaced by the T715, but neither fuze is now on order. The fuzes are similar in construction, except that the T715 allows for varying the arming time by an adjustable setting pin, whereas, in the T84 series, each modification has a fixed setting. Both fuzes have the heavy brass inertia weight and tapered firing-pin housing, so that slight sidewise impact, when armed, will release the cocked firing pin. The drive shaft from the vanes to the gear system is mounted in ball bearings. The locating clip is an assembly feature, to hold the inertia housing in place.

On the T715, arming time is set by varying the depth at which the setting pin is scre-wed into a drive dog. A special key is supplied with the fuze to insure accurate settings. The setting pin is slowly threaded out as the gears turn it, and, when it comes out of the dog, the fuze begins to arm itself. Following is a table of settings:

	Sepcial Screw Driver Depth (Inches)	Arming Distance (Miles)
	0.03	4
	0.10	11
	0.20	23
	0.30	34
	0.40	45

Operation: Vane rotation through the reduction gear train turns a drive disc, the the same time rotating a threaded gear and backing the threaded setting pin out of its drive dog. When the setting pin comes out, a spring shoves the dog toward the drive disc, lat-ching the shaft hub to the drive disc, so that further turning of the drive disc will turn the arming shaft. Turning the arming shaft threads it out of the striker sleeve. The fuze is now fully armed, and impact will cam the striker sleeve dwon against the sleeve spring, freeing the balls and allowing the cocked firing pin to be shot into the primer detonator.

Remarks: Few of these fuzes were made.

The T715 is the companion fuze for the Athwartship Electric Contact Fuze T705; the T84, for the Athwarpship Electric Contact Fuze T74 or corresponding modification.

Figure 404. Athwartship Fuze T715