CHAPTERII, SECTION 1 of cable pairs and reduced the size requirements for the vaults. Comparison of Engineering Design with Previous Operations A new method for the design of non-ex- pendable, blast-resistant structures was adopted for Operation HARDTACK.Prior to Operation HARDTACK, non-expendable structures were designed on the basis of allowable stresses for wind load: i. e., for allowable static load stresses increased by one-third. The new method applied principles as outlined in the ASCE publication, “An Engineering Approach to BlastResistant Design.” The system was basically an “ultimate design” method using considerably higher allowable stresses than for wind load. The net effect of the new design method wasto reduce re-inforcing steel sectional areas and wall and slab thickness. By reason of this effect and the lack of experimental field data, a factor of safety of two was usually applied, but depending on the nature of the structure size and the test evaluation importance for some extremely high psi loading, the factor of safety was reduced in some cases to as low as 1.5. It is anticipated that Operation HARDTACK post-shot damage inspection reports will supply valuable information to the Design Engineers to alleviate questionable design considerations and will lead to more certain and economical blast-resistant design method standards. The scope of engineering design for Operation HARDTACK was more extensive in quantity and variety than for past Operations. This is attested in part by the greater numberof drawings prepared. PAC Construction design require- ments resulted in the preparation of design drawings for the construction of many more categories of permanent base facilities, several of which were extraordinarily large and unusual. The design program for Scientific and Expendable Construction required less complex engineering analysis and planning than the PAC program. In addition, experience gained from previous Operations and the systematic use of the new blast load design method contributed to the moreeffective and expeditious scientific design. The fact that the extent of the design detail and the number of design drawings were greater can be at- tributed to the greater numberof test-shots for Operation HARDTACK as compared to REDWING; preparations for participation of the ABMA missile project at Site How which was subsequently moved to Johnston Island; and the considerable number of facilities developed at Site Nan. Operation HARDTACK notably excluded steel tower zero stations but generally supplanted this shot vehicle with modified U.S. Army BC- type Deck Cargo Barges and LCU hulls. The development of Shot Barge plans for LASL and UCRL required considerable plan details and detail design for four barge types. New or modified major Scientific Stations designed of re-inforced concrete surpassed the extent of overall detail design requirements for other recent Operations because of the greater number of new stations designed in this category. The development of re-inforced concrete structures at Eniwetok Atoll was predominant on Sites Yvonne, Gene, Helen, Irene, and Janet and at Bikini Atoll on Sites Peter, Sugar, Tare, How, Dog, Charlie, and George. Liaison With Jobsite The principal liaison between Home Office and Jobsite Engineering was accomplished by Engineering Work Orders and Contract Authorizations. The Engineering Work Order copies to Jobsite were not only a direct means of conveying detailed information pertaining to the scope of design planning performed by Home Oftice Engineering but in some cases assigned engineering action to be accomplished by Jobsite Engineering. The Contract Authorization documents were mainly to authorize Jobsite camp maintenance and operations and miscellaneous construction projects for which action was requested of Jobsite Engineering by the AEC Chief, Eniwetok Branch Office. They also served to keep Home Office Engineering informed of the scope of Jobsite Engineering action that might be cor- related with Engineering Work Orders. The main line of liaison of correspondence was teletype messages. This medium was used extensively by the Chief Project Engineer and the Resident Engineer to expedite information requests, clarification of details, status of work, and plan changes. TDYvisits were made by the Engineer- ing personnel, as required, to correlate Home Office and Jobsite efforts. Liaison With Users Design criteria were obtained from the Users by means of letters, often with plan sketch descriptions of required new facilities or modifications to existing facilities. All criteria letters requiring design and engineering action were documented by the Project Engineers with the issuance of Engineering Work Orders for each facility project. The Project Engineers assigned to the various Users in a liaison capacity effectively expedited their respective design program from original criteria to issuance of final approved drawings by continuous contact with the various User representatives to discuss their de- sign and engineering requirements. In this manner, new design planning was anticipated in advance of receipt of first criteria letters; status of current design projects became known; and design completion date requirements were planned. Action was then initiated for field tests or surPage 47