Why Ukraine needs U.S. intel even for known targets: How Tomahawk guidance works

Defense Express discussed the issue.

Amid more serious talks about supplying Tomahawks to Ukraine — since the U.S. even has spare launchers — the question of what additional intelligence is needed to strike targets whose coordinates are already known is back in the public sphere.

To answer that, the public needs to understand how the Tomahawk’s navigation and guidance systems work, how other cruise missiles operate, and how their effective use is ensured.

According to the outlet, major cruise missiles combine several navigation systems whose fused data enable precise routing and targeting. The primary system is an inertial navigation unit that calculates position from flight time, speed, and heading.

“This system operates autonomously — loosely speaking, like walking with your eyes closed while counting your steps. Naturally, error accumulates: the longer the missile flies, the larger the error, and even in modern, very expensive high‑precision systems with laser gyros it is about 0.1–0.5%, meaning a 1,000 km flight can yield a 1–5 km deviation,” the analysts explain.

However, the missile’s navigation error can be corrected using terrain. Before satellites, a terrain‑contour navigation system TERCOM was developed in the 1960s, storing terrain elevation snapshots in memory. The missile measures heights during flight and compares them with the reference to adjust its course.

TERCOM works only over terrain with distinctive relief. For deserts or steppes, missiles use DSMAC, which compares photos of the ground to stored reference images. Tomahawk uses both systems to ensure precise targeting across varied landscapes.

In addition, for these systems to function, a high-precision elevation map and current satellite imagery of Russia are needed — both of which can only be reliably provided by the United States.

After TERCOM and DSMAC came satellite navigation. The U.S. indeed has a “military” GPS — encrypted Y‑ and newer M‑codes resistant to spoofing (forging them would require decryption). M‑code is roughly 100× stronger than civilian signals, making jamming unlikely. Tomahawk and other U.S. cruise missiles use this military GPS.

“Good news for Ukraine — the delivery of cruise missiles with 'military' GPS has already been approved, since cruise missiles under the ERAM program are to use that GPS,” the outlet noted.

Another crucial intel layer is air‑defense locations: cruise‑missile flight paths must avoid SAM positions, and the U.S. — via its satellites and other means — holds that data.

“So, overall, when people talk about ‘intelligence’ from the U.S. for cruise‑missile strikes on Russia, it very likely means not the targets’ coordinates but high‑precision maps and imagery formatted for the TERCOM and DSMAC systems used in American cruise missiles,” Defense Express concluded.