The region between the southern tip of the Indian subcontinent and the equator links the Arabian Sea and the Bay of Bengal. A significant exchange of mass, heat and salt occurs in the region via two major current systems: the monsoon current (dominant annual cycle) and the equatorial current (dominant semi-annual cycle). This paper presents observations from deep-sea mooring programmes and describes the rationale for maintaining a mooring array along 77.4°E to monitor both current systems. Analysis shows that the semi-annual to annual cycle transition occurs at 2–2.5°N, with the winter monsoon current peaking at 5°N, the summer monsoon current at 3–6°N, and the equatorial current at 0–1°N.