India’s Defence Research and Development Organisation (DRDO) is advancing its underwater sensing capabilities, with its Naval Physical and Oceanographic Laboratory (NPOL) seeking 10 sets of VLH-1000 hydrophones through a recently issued tender. The procurement focuses on two variants of the underwater acoustic sensors and reflects the continuing importance of indigenous technology in strengthening India’s maritime security capabilities.
According to the reported tender details, NPOL issued the procurement notice on October 23, 2026, under reference number NPOL/27SOT108/LP. The requirement comprises five Type-I hydrophone sets with a diameter of 124 mm and five Type-II sets measuring 94.5 mm. The bid submission deadline is November 10, 2026, while the opening of technical bids is scheduled for November 11. The estimated contract value has not been publicly specified in the available reports.
Hydrophones are specialised underwater acoustic sensors that convert sound pressure into electrical signals for monitoring and analysing underwater noise. In naval applications, these sensors can help detect acoustic signatures generated by ships, submarines and other underwater sources. Their effectiveness depends on factors such as sensitivity, operating frequency, deployment conditions and the signal-processing systems used alongside them.
The VLH-1000 requirement specifies the use of lead zirconate titanate (PZT) ceramics, a piezoelectric material commonly used in acoustic transducers. These ceramics respond to mechanical vibrations by generating electrical signals, enabling the detection of underwater sound. The reported design also includes Grade-2 titanium housings, fibre-reinforced plastic washers and mild-steel moulds. Such materials play important roles in the structural design and durability of equipment intended for demanding marine environments.
The two hydrophone variants feature different dimensions, which may allow them to serve different integration or acoustic requirements. However, detailed performance parameters, including sensitivity ratings, frequency response, maximum operating depth and pressure tolerance, have not been established in the publicly available tender summaries. Their specific deployment configuration and intended platforms have also not been confirmed.
For the Indian Navy, underwater acoustic sensing is an important element of anti-submarine warfare (ASW) and maritime domain awareness. Passive acoustic sensors listen for sounds produced by underwater vessels rather than transmitting their own detection pulses. This approach can support discreet monitoring, although identifying and tracking a submarine generally requires detailed acoustic analysis and, where available, information from additional sensors.
The procurement also highlights the role of NPOL in India’s broader naval technology development programme. Based in Kochi, NPOL is part of DRDO’s Naval Systems and Materials cluster, which works on technologies including sonar, underwater sensors and surveillance systems for the armed forces. Developing domestic expertise in these areas can help India build specialised equipment suited to its operational requirements while reducing dependence on overseas sources for critical components.
The latest tender should be viewed as a procurement step rather than confirmation that the hydrophones have been delivered, qualified or inducted into operational service. Further details about contract award, manufacturing arrangements, testing and eventual deployment have not yet been confirmed in the available reporting.
As India continues to invest in indigenous defence research, underwater acoustic technologies remain a strategically significant area. The outcome of NPOL’s VLH-1000 procurement process may provide further insight into the development and sourcing of homegrown sensors for future naval surveillance requirements.
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