When the MiG-31 entered service in 1981, Western fighters like the F-14 and F-15 still swept the sky with mechanically-rotated radar dishes. The Foxhound’s Zaslon S-800 (NATO “Flash Dance”) had no moving antenna at all: it steered its beam electronically in milliseconds, the first passive electronically-scanned array (PESA) ever fielded on a fighter. It could track around ten targets and engage several at once with the long-range R-33 missile — and, crucially, it could look down and pluck a low-flying cruise missile out of ground clutter, the exact task that had defeated the MiG-25.

Netted together by datalink, four MiG-31s could patrol a barrier nearly 900 km wide across the Arctic approaches to the USSR — each jet feeding the others a shared picture. The modernised Zaslon-M of the MiG-31BM is claimed to reach much further still, feeding today’s very-long-range R-37M. Treat the biggest range numbers with caution, but the through-line is real: from the Cold War Foxhound to the missile-truck of the 2020s, the Foxhound has always been a radar first and an airframe second.

The MiG-25’s R-15 turbojets were optimised for one thing — a flat-out Mach 2.8 dash — and they drank fuel so fast that sustained high-speed flight risked damaging them. The MiG-31’s Soloviev D-30F6 afterburning turbofans changed the equation: more efficient at cruise, they let the Foxhound hold Mach 2.83 at altitude and reach out to a combat radius of around 720 km at high speed, or roughly 1,450 km subsonic. It is the difference between a sprinter that must dash and recover, and an interceptor that can actually patrol.

A single MiG-31 is formidable; four are a system. Using the APD-518 datalink, a flight of four Foxhounds could space themselves out and share a single fused radar picture, sweeping a corridor almost 900 km wide across the northern approaches to the Soviet Union. One jet could detect a target and hand it to another to engage. In an era when Western fighters still fought largely as individuals, this networked, look-down barrier was a genuinely radical piece of air-defence doctrine — and it is the direct ancestor of the datalinked missile-launch tactics Russia uses with the R-37M today.

Hard numbers for the MiG-31 are scarce and unreliable. It was and remains a Soviet-then-Russian state product that was never openly exported, so there is no export price list to anchor an estimate. Figures circulating online range from soft estimates of roughly $30–50 million per airframe to an often-repeated but unsourced “$100 million” — treat all of them as guesswork. No credible cost-per-flight-hour figure exists in open sources either. What is certain is that the MiG-31 is un-buildable: production ended in 1994 and cannot be restarted, so every jet lost is gone for good — a fleet Russia keeps flying precisely because it can no longer make more.