low reliability, and these measurements should provide a better check on the computations. Furthermore, data are lacking for cumulative deck thicknesses greater than about 2 inches. Measurements beneath added thicknesses of 2 inches and 4 inches of steel will provide a check on calculations for ships with armored decks. Superstructure data will aid in the formulation of methods for predicting shielding factors in superstructure compartments. 1.6.6 Bikini data are inadequate for checking the validity of computations for the shielding from airborne activity. These measurements should provide such a check, for locations below the weather deck and in superstructure compartments. 1.6.7 Since the photon energy may change appreciably with time, affecting the transmission of radiation to interior compartnents, the effective energies for transmission through steel can be estimated, as a function of time, by plotting absorption curves from continuous radiation~ time measurements inside a series of steel pipes of various thicknesses mounted on deck, Since preferential removal of certain isotopes by the washdown system could affect the energies, these measurements will be made in the same way on both ships. 2. MISSION 2-1 To obtain informtion necessary to determine the natural gamma raGiation shielding of ships' structures from radioactive material envelop-~ ing the ship and from radioactive material dsposited on weather surfaces. 2-2 To obtain information necessary to compute the hazard from these two sources to personnel within naval vessels either equipped or not equipped with washdown systems. Se TASS AND PLAN OF ATTACK 3.1 Radiation-Time Measurements Continuous dose rate measurements will be made at exposed lorestions on various decks in connection with Project 6.4a. These measure- ments give the total dose rate from all sources at unshielded locations. In addition, an estimate of the dose rate from airborne material surround- ing the ships during the contaminating event will be made using detectors mounted at the top of a mast. From these measurements, the unshielded dose rate from airborne activity and from deposited activity can be evaluatec, as a function of time, for both TRANSIT ABLE and BAKER. sre given ia Annex A.) ST. LOUIS FAC (Details Continuous dose~rate measurements will be made inside various compartments at locations shown in Tab A. In addition, to provide data for larger deck thicknesses than are available on these vessels, two five foot square steel plates have been mounted on TRANSIT BAKER, as shown in Tab A, of 2 inch and 4 inch thickness. After the vessels have emerged from the contaminating event, the ratio of these dose rates to those J2Y