The first letter of interest is dated 14 Jan. 58 and is the last such letter from York as Director to Fidler. the following major headings: P.P The lab programs are broken down into Fundamental research; general weapons research; specific device research and development; specific weapons development and engineering (on which this lab is in the early phases of building up a capability); test planning and evaluation; non-military uses (Plowshare had been initiated); and other programs (Sherwood and nuclear propulsion-Pluto). Note that in the area of specific device R and D, some fair amount of thought and design is going into cleaning up the devices| In the area of planned tests, 3 series are outlined for 58: 58A at the NTS in the spring to include 1. point test only; Hardtack at the EPG and 58B listed for NTS in the fall and including 1 point and full-scale tests. All of these 58 B tests are to be done underground and the s ' ne, tentative list includes 5 full-scale tests,:i: It is stated that "By increasing the yields of devices tested by a factor of 20 or so each time, it is hoped to reach the megaton range in underground testing by 1959. The radio-chemical measurements available in such tests remain subject to question, but accurate yield and prompt diagnostics appear from the Rainier test to be possible. It is hoped that most or all of the UCRL tests for Operation Trumpet (planned for 59) may be carried out in this way. To insure that this canbe planned with assurance, a 20~40 Kt. yield shot should be made in the fall of 1958." Note that planning at this stage for Trumpet includes some evacuated pipe x-ray measurements underground.