Grey-Zone Drills

What it is

Grey-zone drills are military and paramilitary exercises designed to rehearse coercive operations that fall below the threshold that would trigger a conventional military response or invoke formal alliance commitments. Unlike standard war games, they combine regular military forces, coast-guard vessels, maritime militia, cyber units, and information operations to create deliberate ambiguity about intent and attribution. The US DNI's updated Intelligence Community Gray Zone Lexicon, published July 2024, defines the grey zone as the "competitive space between routine statecraft and open warfare." Actors conducting these drills seek to shift facts on the ground, erode adversary resolve, and avoid clear-cut acts of force that would justify a formal military reply.

The principal practitioners as of mid-2026 are China (targeting Taiwan, Japan's Senkaku Islands, and South China Sea claimants), Russia (targeting NATO's eastern flank through shadow-fleet harassment, Baltic airspace probing, and sabotage attributed to GRU units), and North Korea (calibrated missile tests and oil-smuggling runs designed to impose costs without triggering collective-defence obligations).

History

The concept solidified in US strategic literature after Russia's 2014 annexation of Crimea and China's island-building campaign in the South China Sea demonstrated that great-power rivals had moved below the deterrence threshold of conventional military tools. A RAND Corporation study formally defined the grey zone as an "operational space between peace and war" in which coercive actions change facts on the ground while "blurring the line between military and non-military actions." The UK Parliament's Defence Select Committee reached a parallel conclusion in its own inquiry, finding that both Russia and China had developed grey-zone capabilities specifically calibrated to exploit gaps in NATO and allied legal authorities.

China's grey-zone campaign against Taiwan began in earnest after the 1996 Taiwan Strait Crisis, when US carrier battle groups deterred PLA action and Beijing resolved to develop tools harder to counter with carriers. The PLA's August 2022 exercises, triggered by then-US House Speaker Nancy Pelosi's Taipei visit, marked a doctrinal shift: for the first time the PLA established de-facto exclusion zones that Taiwan and its partners treated as a new permanent baseline rather than a one-off provocation.

Current state

China's campaign against Taiwan is the most data-dense grey-zone as of mid-2026. PLA aircraft entered Taiwan's air-defense identification zone more than 3,700 times in 2025, the highest annual total on record. The Chinese coast guard spent 335 consecutive days patrolling waters around Japan's Senkaku Islands in 2025, shattering the previous record of 215 days. "Justice Mission 2025," the sixth major PLA exercise simulating a Taiwan blockade since 2022, closed inside the perimeter of previous exercises (see 中国空母打撃群が台湾海峡を通過、5日間の封鎖演習が最高潮に and 中国空母「福建」、米同盟国のバリアント・シールド演習中に12月以来初の台湾海峡通過). China's grey-zone fleet operates as an ecosystem: coast-guard vessels, maritime militia fishing boats, sand dredgers, and opaquely owned cargo ships, all used to harass and probe while stopping short of armed conflict.

Allied counter-pressure has intensified. The US, Japan, Australia, and the Philippines mounted coordinated coast-guard patrols in June 2024 (see 米英仏独、台湾東方沖での中国海警の哨戒を巡り初の共同警告を発出). Taiwan has reframed its response to prioritise cost-imposition, including detaining vessels implicated in undersea cable sabotage and increasing transparency about Chinese incursions to delegitimise Beijing's narratives.

Relationships

Grey-zone drills are the operational expression of the rivalries tracked in Taiwan Strait: they test alliance credibility, drive demand for counter-measures such as electronic warfare and AI-enabled attribution, and feed into the deterrence debates rehearsed in 台湾、初の「海上威圧対応」と明示した図上演習を実施. Because grey-zone activity is designed to remain below the formal threshold of conflict, it consistently outpaces the legal frameworks and rules of engagement that defenders rely on. RUSI's March 2025 analysis found Taiwan's core vulnerability is diplomatic isolation, which discourages escalatory responses and makes coalition-building with other grey-zone targets the most actionable path.

What to watch

• Whether the PLA's 2026 exercises expand beyond the normalised perimeter that "Justice Mission 2025" established around Taiwan, or extend into the Philippine Sea.
• US Indo-Pacific Command's response to China's record Senkaku coast-guard presence as Japan invokes its expanded self-defence authorities under the 2022 National Security Strategy.
• Taiwan's progress on RUSI's recommendation to build a regional grey-zone coalition sharing attribution intelligence, with the Philippines, Japan, and Australia as the core.
• Whether China's 2021 coast-guard law, authorising lethal force in claimed waters, is invoked against a US or allied vessel in the Senkaku or Spratly theatres.