brought back to Los Angeles to be used in revising H & N tracings. NOBEL stated that 21 field panels would be required; 18 for the Field, 2 spares, and one to be delivered as a sample to NOL. Also at this meeting various other items of special equipment required by NOBL were discussed, and prints of NOL drawings were given to H & N to use in preparing drawings for these items. These included velocity instrument posts and two different types of ball crusher gauge mountings. NOBL stated that a total of 44 instrument posts, 150 steel stake gauge mounts, and 15 concrete gauge mounts (12 for Field, 2 spares and 1 for NOL) would be required, The velocity instrument post was an assembly consisting of a piece of curved 3-inch pipe cast in a concrete block set flush with grade, with a 3-inch pipe extending approximately 10 feet in the air above grade. One type of ball crusher gauge mounting (concrete gauge mount) con- sisted of a 30~inch square steel plate, 3 inches thick, machine-grooved to a depth of 11/2 inches to receive a 4-inch wide by 33 1/2-inch long steel plate, which was held in assembly with the larger plate by means of a pos- itive latching device at each end, Four 1 1/2-inch diameter holes were bored in the smaller plate, and four 2 1/4~inch diameter by 18-inch steel cans fastened to the larger plate, to receive the ball crusher gauges fur- nished by the User (NOBL). In the Field, this assembly was to be set flush with grade and anchored to a 6-foot deep concrete block by means of twenty-four 3/8-inch diameter anchor rods fastened to the underside of the 3einch thick steel plate. The steel stake gauge mount consisted of a 6-foot long, 2-inch diam~ eter steel stake, tapered at one end and threaded at the other end to receive a threaded steel cap. In the Field, this assembly was to be installed by driving it into the ground as far as the threaded cap, which was then to be removed and replaced with a ball crusher gauge furnished by the User (NOBL). On February 10, 1950, H & N was instructed verbally by J-Division to prepare final engineering drawings for the entire group of previously men- tioned NOBL special assemblies, These drawings were prepared, and prints of them were sent to J-Division on February 16, 1950 for approval. H & N was also instructed to proceed with the manufacture of one field panel, one steel stake gauge mount, and one concrete gauge mount and have them sent to NOL at Silver Spring, Md. However, on February 20, 1950 instructions were received by telephone to hold up fabrication of the field panel (blast wall tank) until further notice, as the design would probably be changed. This was confirmed in a letter of February 24, 1950. By let- ter of March 6, 1950 H & N was instructed to fabricate one field panel and deliver it to NOL, Silver Spring, Md. By letter of April 17, 1950 H & N received sketches of an additional assembly required by NOBL. This was a gauge mounting plate, consisting of a rectangular steel plate (18 inches by 12 inches by 1 inch thick). This plate was blank, except for eight 3/8-inch drilled and tapped holes and eight anchor rods to anchor the plate to a concrete base in the Field. 5-180