ship for crater depth may approach the fourth root; this conforms with the craterprediction curves in Reference 7 (Figures 32, 33, 34, and 35).
Thus, especially based on the conclusions derived in Reference 10, (made partially
possible by the data of Castle Project 3.2) considerable increase in reliability has re~
sulted with respect to predictions of craters produced by megaton detonations.
4.3
TREE-STAND STUDIES
Operation Castle presented an opportunity to make measurements on natural tree
stands several times larger than the Operation Upshot-Knothole experimental tree stand.
Even though the natural stands were composedof tropical trees found at the EPG, breakage data was considered desirable, since continental tests in forested areas were not
planned.
During Upshot-Knothole, an artificial stand of trees 320 feet long by 160 feet wide
compos 2d of 145 Ponderosa pine trees averaging 51 feet in height, had been exposed at
a 4.5-psi peak static overpressure. The stand was instrumented elong its length and
across its width with ground-level static-overpressure gages, as well as dynamic-
pressure gages at three elevations located 250 feet from the front of the stand. Groundleve] pressure measurements had showed no significant attenuation in peak static
overpressure or increase in rise times.
Upshot-Knothole results had also indicated that the prediction system for isolated
trees was conservative when applied to small coniferous tree stands.
However, in view
of the unknown degreeof attc nuation for large stands and the tenuous nature of military-
damagecriteria for trees, damage predictions for isolated trees were assumed representative for tree stands. Thus, from all available data, a general breakage-prediction
system had been developed that represented various levels of breakage probability for
tree stands. The prediction system could be applied to idealized tree stands to determine
damage by various-yleld weapons, using height-of-burst curves modified to include wave
form, where damage criteria were based on length of stem down per acre. Forthree
general tree-stand types, isodamage curves giving light and heavy damage had been prepared for inclusion in TM 23-200 (Reference 7).
Sample plots were selected on three small, naturally forested islands of Bikini Atoll —
Uncle, Victor, and William.
These islands spanned a desirable predicted-overpressure
region for the expected yield from Shot 3 ranging from heavy damage to light or no damage. It was essential that a substantial portion of the trees remain intact as a group,
giving a graded series of damage to correlate with the previously developed tree-breakage
prediction system.
In spite of the unexpected low yield of Shot 3, Project 3.3 achieved basic damage data.
The unexpectedly large yield of Shot 1—blast incident from the opposite direction of
_
Shot 3—caused heavy damage to the tree stands on William and Victor Islands and light
damageto the upper portion of the stand on Uncle Island. Shot 2—Dblast incident from
the same direction as Shot 1—-caused no additional damage. The Shot 1-Shot 3 situation
proved to be very fortunate. Because of the opposite directions of blast incidence and
extreme yield difference, heavy damage from Shot 3 only extended to just beyond the
light damage region of Shot 1. Thus, two sets of graded’ damage data were secured in- stead of one: from a high-yield device with long positive-phase duration (15.0 Mt, 2.5-psi
peak static overpressure, 10-second positive-phase duration) and from a medium-yield
device with shorter positive-phase duration (130 kt, 4.5-psi peak static overpressure,
1.2-second positive-phase duration).
The principal tree growth on the three islands selected consisted of five main compo66