The United States has instructed oil tankers navigating the Strait of Hormuz to transit only during specific time windows to receive military protection, following an increase in nighttime attacks on vessels. Since May, Washington has offered aerial defenses for ships choosing to sail along the southern route near Oman's coast, shielding them from Iranian strikes and allowing some crude exports to leave the Gulf.

Ship owners must submit requests to the U.S. Navy's Shipping Coordination Center (the naval cooperation and guidance body, known as NCAGS), which then provides navigational coordinates to crews and permits passage within broad nighttime hours. During this period, vessels come under the protection of American fighter jets. Emails from NCAGS to maritime advisors, seen by the media, indicate that in early September, these transit windows were tightened to two specific periods each day. Vessels were told to depart at designated times, such as 9 a.m. One email stated: "We currently offer daily adjusted recommended transit times. Vessels are not obligated to sail within this window, but it is advised for optimal protection." Another email noted that, given the threats facing commercial ships, "transiting at night has proven not to be the safest part of the day."

The U.S. Central Command, which oversees American military operations in the Middle East, stated that the content of NCAGS's emails speaks for itself. Since the U.S. and Israel struck Iran in February, Iranian armed forces have attacked dozens of vessels attempting to use the contested waterway, aiming to assert control. This adjustment of convoy protection to set day and night periods comes as both Washington and Tehran escalate their campaigns against commercial shipping. Iran said early Wednesday that it had struck two U.S. vessels and eight tankers in response to U.S. attacks on five Iranian tankers. The U.S. military attributed this Iranian retaliation to a prior strike by Iran's Islamic Revolutionary Guard Corps, which used ballistic missiles against an American warship earlier in the week. The U.K. Maritime Trade Operations office also reported on Wednesday that Iran had attacked multiple tankers off the coasts of Dubai and Iraq.

Joshua Tallis, a naval analyst at the U.S. security research institute CNA, suggested that requiring vessels to transit at specific times is likely an effective way to "manage the costs of a long-term, indefinite U.S. defense of the southern route through the Strait of Hormuz." Tallis noted that advanced U.S. military aircraft cost between $25,000 and $75,000 per flight hour. A maritime security advisor serving the Gulf shipping industry commented that concentrating military resources in shorter periods, rather than covering twelve hours of darkness, allows the U.S. to "muster more force and achieve better protection." A merchant ship transiting the strait at slow to medium speed takes approximately seven hours. It is understood that Iran's Islamic Revolutionary Guard Corps deploys small patrol boats to hunt for vessels taking the Omani side, which often sail at night with their GPS signals and navigation lights switched off.

Since the conflict began on February 28, more than 70 commercial ships have been attacked. Iran announced on Monday its intention to establish a "restricted zone" in the strait. Mohsen Rezaei, Secretary of Iran's Supreme National Security Council, stated the area "starts from the U.S. maritime blockade line, extends to the Strait of Hormuz, and from there continues into the Persian Gulf." Tehran has said any vessel entering this zone will face "sanctions," though it has not specified what those would entail. Iran also indicated that a preliminary agreement with Oman on future management of the strait is close to completion. However, shipbroker Clarksons said on Monday that disruptions to shipping through the waterway are unlikely to ease until at least the second half of 2027.

Retired Vice Admiral John Miller, a former commander of U.S. naval forces in the Middle East, commented on the transit window adjustments: "If we are going to conduct this operation over the long haul, properly allocating military assets and maintaining operational sustainability will be critical." He added that providing round-the-clock air cover on a permanent basis "is extremely difficult to execute," so the U.S. "must establish rules."