This paper presents results from a survey of lambda 21-cm emission from galaxies in the Hercules cluster, A2151 and A2147. Four VLA primary beam areas were covered, a total area of 0.9 square degrees, including some 120 spiral galaxies brighter than 17.5m. The velocity resolution is 44km/s, the angular resolution 25". The detection threshold at field center is 2.6x10^8 h^{-2}M_{sun}_ in H I mass or about 1.8x10^20cm^-2^ in column density. There are 61 galaxies detected in H I, of which about 25 had been previously detected at lambda 21-cm. About ten of the detections correspond to galaxies that are very faint in the optical, m_E_>=18 or M>=-17mag-5logh. Some of these low surface brightness galaxies have very extended H I disks, with r>=15kpc. The abundance of H I is a strong function of position in the cluster, with galaxies in the south and west showing hardly any gas, and galaxies in the north and east of A2151 frequently having massive, extended gas disks. The morphology of the remnants of gas in galaxies in the south and west suggests that the intracluster medium is responsible for their H I deficiency, but there are also several dramatic galaxy mergers in progress. (c) 1997 American Astronomical Society.