Operation Hardtack I
Umbrella blast
June 9 saw the second underwater nuclear test of the Hardtack I series. The detonation occurred at 11:15 AM (local time) with clear skies and a 15 to 17-knot wind from the east-northeast.

Operation Hardtack I

Section Title: Umbrella blast
Table Section Text: June 9 saw the second underwater nuclear test of the Hardtack I series. The detonation occurred at 11:15 AM (local time) with clear skies and a 15 to 17-knot wind from the east-northeast.

Name	Date time (UT)	Local time zone	Location	Elevation + height	Delivery Purpose	Device	Yield	References Notes

Yucca	April 28, 1958 02:40:00.3	edst (12 hrs)	Pacific Proving Grounds 12°37′01″N 167°01′30″E / 12.617°N 167.025°E	0 + 26.21 kilometres (16.29 mi)	balloon, weapon effect	W-25	1.7 kt	ABM development - part of Operation Newsreel (high altitude tests). Fired "about 85 nmi (157 km; 98 mi) northwest of Bikini".

Cactus	May 5, 1958 18:15:00.1	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°33′09″N 162°20′50″E / 11.55255°N 162.34727°E	1 m (3 ft 3 in) + 1 m (3 ft 3 in)	dry surface, weapons development	Mk-43 primary	18 kt	LASL test of a MK-43 primary in a thermonuclear system mockup. Similar to Elder.

Fir	May 11, 1958 17:50:00.1	MHT (11 hrs)	Namu (Charlie), Bikini Atoll 11°41′27″N 165°16′24″E / 11.6908°N 165.2733°E	0 + 3 m (9.8 ft)	barge, weapons development	1.4 Mt	Clean 2-stage TN device, only 90 kt fission, 93.4% fusion yield.

Butternut	May 11, 1958 18:15:00.1	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′19″N 162°20′37″E / 11.53859°N 162.34367°E	0 + 3 m (9.8 ft)	barge, weapons development	TX-46 primary ?	81 kt	TX-46 primary test, similar to Oak and Yellowwood.

Koa	May 12, 1958 18:30:00.1	MHT (11 hrs)	Teiter (Gene), Enewetak Atoll 11°40′12″N 162°11′54″E / 11.66997°N 162.19847°E	2 m (6 ft 7 in) + 0.81 m (2 ft 8 in)	dry surface, weapons development	XW-35	1.4 Mt	XW-35 ICBM warhead test.

Wahoo	May 16, 1958 01:30:00.5	MHT (11 hrs)	Pokon (Irvin), Enewetak Atoll 11°19′35″N 162°09′47″E / 11.32646°N 162.16309°E	0 - 150 m (490 ft)	underwater, weapon effect	Mk-7	9 kt	Mk-7 deep underwater explosion effects, water depth 3,200 ft (980 m).

Holly	May 20, 1958 18:30:00.1	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′25″N 162°21′01″E / 11.54029°N 162.35039°E	0 + 4 m (13 ft)	barge, weapons development	XW-31Y3	5.9 kt	XW-31Y proof test.

Nutmeg	May 21, 1958 21:20:00.2	MHT (11 hrs)	Eninmen (Tare), Bikini Atoll 11°30′13″N 165°22′20″E / 11.50355°N 165.3722°E	0 + 3 m (9.8 ft)	barge, weapons development	early XW-47 ?	25.1 kt	2 stage thermonuclear device, possible W47.

Yellowwood	May 26, 1958 02:00:00.1	MHT (11 hrs)	Enjebi (Janet), Enewetak Atoll 11°39′27″N 162°13′18″E / 11.65751°N 162.22168°E	0 + 3 m (9.8 ft)	barge, weapons development	TX-46, became W-53	330 kt	LASL developmental test of a "clean" TX-46 warhead design. Fizzled, low burn in secondary. Retry in Oak.

Magnolia	May 26, 1958 18:00:00.1	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′22″N 162°20′54″E / 11.53932°N 162.34841°E	0 + 4 m (13 ft)	barge, weapons development	"Cougar"	57 kt	Proof test.

Tobacco	May 30, 1958 02:15:00.2	MHT (11 hrs)	Enjebi (Janet), Enewetak Atoll 11°39′38″N 162°13′36″E / 11.66056°N 162.22663°E	0 + 2.7 m (8 ft 10 in)	barge, weapons development	XW-50	11.6 kt	Exploratory shot, XW-50 Nike-Zeus prototype, 2nd stage failed to ignite.

Sycamore	May 31, 1958 03:00:00.1	MHT (11 hrs)	Namu (Charlie), Bikini Atoll 11°41′50″N 165°16′29″E / 11.69722°N 165.27486°E	0 + 3 m (9.8 ft)	barge, weapons development	TX-41	92 kt	"Clean" TX-41 fizzle; predicted yield 5 Mt total, 200 kt fission; low level burning in 2nd stage; similar to Poplar and Pine.

Rose	June 2, 1958 18:45:00.1	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′21″N 162°20′45″E / 11.53926°N 162.34593°E	0 + 4.5 m (15 ft)	barge, weapons development	XW-49 ? Primary	15 kt	Exploratory shot, possible XW-49, 80 kt fusion expected, 2nd stage failed to ignite.

Umbrella	June 8, 1958 18:15:00.2	MHT (11 hrs)	Pokon (Irvin), Enewetak Atoll 11°22′30″N 162°11′38″E / 11.37498°N 162.19399°E	0 - 50 m (160 ft)	underwater, weapon effect	Mk-7	8 kt	Shallow underwater explosion on lagoon bottom at 150 ft (46 m). Crater 915 m × 6 m (3,002 ft × 20 ft).

Maple	June 10, 1958 17:30:00.1	MHT (11 hrs)	Yurochi aka Irioj (Dog), Bikini Atoll 11°41′29″N 165°24′57″E / 11.6915°N 165.41582°E	0 + 3 m (9.8 ft)	barge, weapons development	213 kt	"Dirty" 2-stage test, predicted to be 89% fission.

Aspen	June 14, 1958 17:30:00.1	MHT (11 hrs)	Namu (Charlie), Bikini Atoll 11°41′27″N 165°16′24″E / 11.6908°N 165.2733°E	0 + 3 m (9.8 ft)	barge, weapons development	XW-47 ?	319 kt	Possible XW-47 prototype, 2 stage.

Walnut	June 14, 1958 18:30:00.1	MHT (11 hrs)	Enjebi (Janet), Enewetak Atoll 11°39′27″N 162°13′18″E / 11.65751°N 162.22168°E	0 + 2 m (6 ft 7 in)	barge, weapons development	1.5 Mt	Thermonuclear prototype development test.

Linden	June 18, 1958 03:00:00.1	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′26″N 162°21′04″E / 11.54061°N 162.35106°E	0 + 2.5 m (8 ft 2 in)	barge, weapons development	XW-50 primary ?	11 kt	Possible XW-50 primary.

Redwood	June 27, 1958 17:30:00.1	MHT (11 hrs)	Yurochi aka Irioj (Dog), Bikini Atoll 11°41′29″N 165°24′57″E / 11.6915°N 165.41582°E	0 + 3 m (9.8 ft)	barge, weapons development	XW-47 ?	412 kt	Possible XW-47 prototype, 2-stage, 250 kt fission yield expected; similar to Aspen, Nutmeg, Dogwood devices.

Elder	June 27, 1958 18:30:00.1	MHT (11 hrs)	Enjebi (Janet), Enewetak Atoll 11°39′38″N 162°13′36″E / 11.66056°N 162.22663°E	0 + 2.7 m (8 ft 10 in)	barge, weapons development	TX-43	880 kt	TX-43 laydown bomb test, 50% fission yield expected, similar to Cactus.

Oak	June 28, 1958 19:30:00.1	MHT (11 hrs)	Bogallua (Alice), Enewetak Atoll 11°36′11″N 162°06′09″E / 11.60309°N 162.10259°E	0 + 1.8 m (5 ft 11 in)	barge, weapons development	TX-46/53	8.9 Mt	Prototype test of the LASL designed TX-46 system. Similar to Butternut and Yellowwood.

Hickory	June 29, 1958 00:00:00.9	MHT (11 hrs)	Eninmen (Tare), Bikini Atoll 11°29′46″N 162°22′15″E / 11.4961°N 162.3708°E	0 + 3 m (9.8 ft)	barge, weapons development	XW-47 primary ?	14 kt	Possible XW-47 primary test, similar to Hardtack II Neptune and Titania.

Sequoia	July 1, 1958 18:30:00.1	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′26″N 162°21′04″E / 11.54061°N 162.35106°E	0 + 2 m (6 ft 7 in)	barge, weapons development	XW-50 primary ?	5.2 kt	Similar to Hardtack II Otero, test of Hardtack I Pisonia primary.

Cedar	July 2, 1958 17:30:00.1	MHT (11 hrs)	Namu (Charlie), Bikini Atoll 11°41′50″N 165°16′29″E / 11.69722°N 165.27486°E	0 + 3.4 m (11 ft)	barge, weapons development	220 kt	2-stage "clean" thermonuke device, predicted fission yield 30 kt.

Dogwood	July 5, 1958 18:30:00.2	MHT (11 hrs)	Enjebi (Janet), Enewetak Atoll 11°39′38″N 162°13′36″E / 11.66056°N 162.22663°E	0 + 3 m (9.8 ft)	barge, weapons development	XW-47 ? Piccolo	397 kt	Similar to Redwood, Aspen, Nutmeg; possible XW-47 prototype, Piccolo 2nd stage.

Poplar	July 12, 1958 03:30:00.1	MHT (11 hrs)	Namu (Charlie), Bikini Atoll 11°41′49″N 165°16′01″E / 11.69704°N 165.26708°E	0 + 3 m (9.8 ft)	barge, weapons development	TX-41	9.3 Mt	TX-41 "clean" 2-stage variant; similar to Pine and Sycamore; largest of Hardtack I, and 5th largest U.S. test ever.

Scaevola	July 14, 1958 04:00:??	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′48″N 162°21′07″E / 11.54662°N 162.35199°E	2 m (6 ft 7 in) + 6 m (20 ft)	barge, safety experiment	XW-34	no yield	XW-34 1-point safety test, successful.

Pisonia	July 17, 1958 23:00:??	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°33′N 162°19′E / 11.55°N 162.31°E	0 + 2 m (6 ft 7 in)	barge, weapons development	XW-50 ? TN, sequoiah pr	255 kt	Probable prototype XW-50 thermonuclear design, modified Tobacco device, used Sequoia primary.

Juniper	July 22, 1958 04:20:00.1	MHT (11 hrs)	Eninmen (Tare), Bikini Atoll 11°30′13″N 165°22′20″E / 11.50355°N 165.3722°E	0 + 3 m (9.8 ft)	barge, weapons development	XW-47	65 kt	"Most radical UCRL shot", "entirely new concept", last Bikini atmospheric shot, probable XW-47 candidate.

Olive	July 22, 1958 20:30:00.2	MHT (11 hrs)	Enjebi (Janet), Enewetak Atoll 11°39′38″N 162°13′36″E / 11.66056°N 162.22663°E	0 + 3 m (9.8 ft)	barge, weapons development	202 kt	Concept feasibility test, 2-stage thermonuclear device, established high yield/light weight; weight 100 kg (220 lb) (yield/weight ratio 2 kt/kg).

Pine	July 26, 1958 20:30:00.2	MHT (11 hrs)	Enjebi (Janet), Enewetak Atoll 11°39′05″N 162°12′51″E / 11.6513°N 162.21414°E	0 + 3 m (9.8 ft)	barge, weapons development	Mk-41	2 Mt	TX-41 "clean" 3-stage variant; similar to Poplar and Sycamore.

Piñon (canceled)	August 1958	edst (12 hrs)	Pacific Proving Grounds 12°N 162°E / 12°N 162°E	3 m (9.8 ft) +	air drop, weapon effect	unknown	A proposed international demonstration of a clean thermonuke. Cancelled by President Eisenhower in the runup to the 1958 test moratorium.

Teak	August 1, 1958 10:50:05.6	jamt (-11 hrs) Believed in use during Dominic, Fishbowl,HT I.	Launch from Johnston Island, Johnston Atoll 16°44′01″N 169°31′31″W / 16.73365°N 169.52534°W, elv: 3 + 0 m (9.8 + 0.0 ft); Detonation over Johnston Island, Johnston Atoll 16°44′38″N 169°32′00″W / 16.7439°N 169.5333°W	N/A + 81.3 kilometres (50.5 mi)	high alt rocket (30–80 km), weapon effect	W-39	3.8 Mt	ABM effects test. Miscalculation resulted in detonation directly above launch site.

Quince	August 6, 1958 02:15:??	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′54″N 162°21′03″E / 11.54828°N 162.35079°E	1 m (3 ft 3 in) + 1 m (3 ft 3 in)	dry surface, weapons development	XW-51 ?	no yield	Probable XW-51 test, fizzle.

Orange	August 12, 1958 10:30:08.6	jamt (-11 hrs) Believed in use during Dominic, Fishbowl,HT I.	Launch from Johnston Island, Johnston Atoll 16°44′01″N 169°31′31″W / 16.73365°N 169.52534°W, elv: 3 + 0 m (9.8 + 0.0 ft); Detonation over Johnston Island, Johnston Atoll 16°21′30″N 169°32′08″W / 16.3583°N 169.5356°W	N/A + 45.5 kilometres (28.3 mi)	high alt rocket (30–80 km), weapon effect	W39	3.8 Mt	ABM effects test, W-39 warhead, part of Operation Newsreel (high altitude tests), carried on a Redstone rocket.

Fig	August 18, 1958 04:00:??	MHT (11 hrs)	Runit (Yvonne), Enewetak Atoll 11°32′58″N 162°20′56″E / 11.54955°N 162.34879°E	1 m (3 ft 3 in) + 0.5 m (1 ft 8 in)	dry surface, weapons development	XW-51 ?	20 t	Probable XW-51 test, similar to Quince, successful, last atmospheric shot at Enewetak.

Sentence(s)

Operation Hardtack I produced a 412 kt yield range.

final_sentence: Operation Hardtack I produced a 412 kt yield range.