Twenty-One Miles: The Physical Geography of the World's Most Important Waterway
The Strait of Hormuz is 90 miles long and between 21 and 55 miles wide. The navigable channel — the portion deep enough for laden very large crude carriers and the other substantial vessels that transit it — is much narrower. Two traffic separation lanes, each approximately two miles wide, handle the inbound and outbound commercial traffic, separated by a two-mile buffer zone. The effective transit corridor for a laden supertanker is therefore something on the order of two miles across, within a strait that appears much wider on maps but that shallow water, islands, and navigational hazards reduce to a constrained passage at the critical point.
The depth profile of the strait matters for submarine operations and mine deployment. The Gulf itself is notably shallow — average depths of around 35 meters — which constrains submarine operations and reduces the effectiveness of some mine types. The strait itself is deeper, reaching roughly 70-80 meters in the main channel, before opening into the much deeper Gulf of Oman on the southern side. The transition from the shallow Gulf environment to the deeper Gulf of Oman waters is operationally significant: Iranian submarines transiting from Gulf of Oman operating areas into the Gulf must navigate through the strait, where they are most detectable, before entering the confined shallow waters where their operational constraints are greatest.
The tidal and current patterns of the strait create navigation conditions that are less forgiving than open ocean transits. Strong currents — running at up to four knots at peak tidal flow — require tanker pilots to account for drift on a corridor that offers limited margin for error. Tanker grounding incidents in the strait, most of them unrelated to hostile action, are not rare, and the consequences of a very large crude carrier grounding in the main traffic lane would be severe even if the vessel itself was recoverable. Iranian harassment tactics that force large vessels to deviate from normal routing create an elevated grounding risk that compounds the direct threat from any weapons that might be used.
The islands within and adjacent to the strait have navigational and military significance simultaneously. Qeshm Island, the largest island in the Middle East, sits in the strait on the Iranian side and creates the southern boundary of the narrowest navigable passage. Its shoreline provides observation points, boat launch facilities, and — as Iranian forces have used it — staging areas for fast attack craft that can intercept traffic moving through the adjacent lanes. The Hengam Island, smaller and farther south, has hosted Iranian military facilities that include radar systems capable of tracking all strait traffic. The disputed islands of Greater Tunb, Lesser Tunb, and Abu Musa sit near the entrance where the strait opens into the Gulf of Oman, providing Iranian military presence on the approaches.
The Musandam Peninsula of Oman forms the southern jaw of the narrowest point. Its fjord-like coastline — deep inlets cutting into dramatic limestone mountains — creates a geography that is spectacular but also difficult to monitor from the water. Iranian fast attack craft operating near the Iranian islands can disappear from radar coverage behind Qeshm Island’s bulk. Coalition surveillance systems must maintain coverage of an operating environment where terrain masking is a persistent challenge and where the radar and visual horizon lines that define tactical awareness are compressed by the geography.
The approach routes matter as much as the strait itself. Vessels entering from the Gulf of Oman must navigate the approaches past the disputed islands before reaching the traffic separation scheme. Departing vessels exit past the same islands and must clear the approaches before reaching open ocean. Iranian military assets positioned on those islands have engagement solutions against vessels at all points in the approach and departure sequence, not just within the narrowest part of the strait.
The physical geography was not designed as a military problem. It was made one by the combination of oil deposits on one side and ocean trade routes on the other, intersecting at a point where an ancient tectonic collision produced twenty-one miles of contested water.