The Ocean Weather Ship Weather Reporter, underway from the United Kingdom to assume her position at station J (near 53¿N, 18¿W) on the North Atlantic, encountered heavy seas over a 4-day period from September 12--15, 1961. The ship measured the sea state during this period with a shipborne wave recorder at 3-hour intervals. The wave energy spectra are computed from the records and are presented. The upper and lower confidence limits in the estimation of these energy spectra are discussed. Such statistical quantities as the significant wave height and the average period are presented.