Executive Summary
Modern radar misses a great deal. Low-altitude cruise missiles, Iranian-design Shahed and Russian Geran-3 attack drones, and small first-person-view drones either fly below the radar horizon or present too small a return to confirm in time. Acoustic sensors hear what radar cannot see. Ukraine's Zvook system, also called SkyFortress, links roughly 10,000 mobile-phone-based listening posts that detect inbound Shaheds by engine signature within two to five kilometres and cue Patriot and short-range air-defence crews (RUSI, 2024). Poland's PIT-RADWAR has fielded the Sola acoustic detector against the same threat. Lithuania has no documented equivalent. This is a gap Lithuania should study. Vilnius sits 35km from Belarus; the country covers 65,300 square kilometres; April 2026 cabinet decisions on 48 Merops interceptors, more NASAMS, and Skyranger 30 host-nation arrangements pointed at the kinetic side. The sensor layer that tells interceptors when to fire is missing. The recommended next step is a Ministry of National Defence feasibility study examining whether a Zvook-style citizen mesh, a Sola-style fixed network, or a hybrid fits Lithuanian geography and budget. Scale, sensor type, and integration path are for Lithuania to determine.
The Problem
The threats that reach Lithuanian airspace are increasingly low and slow. The Iranian-design Shahed-136 and its Russian-built Geran-3 jet variant cruise at 300 to 370 kilometres per hour with a service ceiling near nine kilometres, often flying nap-of-the-earth profiles to slip under radar. Russian Kh-101 cruise missiles do the same. Small first-person-view drones present a radar cross-section close to that of a bird. Belarusian and Russian electronic warfare jams the GPS signals these systems navigate by, but also degrades the air-defence radars meant to catch them. Acoustic detection is passive, emits no signal an anti-radiation missile can home on, and works on physics that cannot be jammed.
Lithuania has no publicly documented distributed acoustic sensor layer. Air-defence procurement is concentrated on radar, NASAMS, the German IRIS-T offered through host-nation arrangements, the 48 Merops AS-3 counter-drone interceptors approved on 22 April 2026, the 214-million-dollar AIM-9X buy approved on 24 April 2026, and the 234-million-euro NASAMS additional package. None of those systems hears a Geran engine before the radar paints it.
Lithuanian Context
Vilnius sits 35 kilometres from the Belarusian border. The country covers roughly 65,300 square kilometres, which means full coverage at a Zvook-style two-to-five-kilometre node radius would require thousands of nodes; partial coverage focused on the eastern border, the Suwalki corridor, and approaches to Vilnius and Kaunas would require hundreds. Whether the right form is a citizen-volunteer mesh on the Ukrainian model, a fixed PIT-RADWAR Sola installation on the Polish model, or a hybrid is a Lithuanian determination.