||Navy Underwater Construction Teams require a capability for making access holes through arctic sea ice. Required hold diameters range from less than 4 in. (100 mm) to more than 10 ft (3 m) in ice up to 15 ft (4.6 m) thick. Small diameter holes are to be completed in less than 4 hr. and large diameter holes in less than 8 hr. The report first gives brief descriptions of the working environment, site access considerations, and probable operational procedure. Principles and techniques for penetrating sea ice are summarized, with an initial list of 14 topics. Twelve of these items are identified as potentially relevant, and are discussed more fully. They include: 1) projectile penetration, 2) shaped charge penetration, 3) high pressure water jets, 4) blasting, 5) flame jets, 6) electrothermal devices, 7) hydrothermal devices, 8) rotary drilling, 9) percussive and vibratory penetration, 10) mechanical cutting, 11) chemical penetration, 12) exotic concepts. The final selection, which takes into account practical concerns and field experience, recommends the following things as basic tools: a) small diameter auger drills (less than 4 in diam), b) large diameter auger drills (~9 in. diam), c) chain saws, d) a hot water system for drilling and cutting. The discussion of associated equipment covers electric generators, hoists and lifting tackle, hand tools, and blasting supplies. Consideration is also given to a single-fuel operation, bulk melting, and possibilities for use of compressed air. Recommendations for development work by NCEL are given.