Submarine Communication Systems — Reaching the Deep

VLF is the primary method for broadcasting messages to submarines worldwide. Shore-based transmitters use enormous antenna arrays — NAA Cutler in Maine uses 26 towers across 2,000 acres. Submarines receive VLF by deploying a trailing wire antenna or floating buoy antenna at shallow depth. While data rates are low, VLF can transmit coded messages, weather updates, and emergency action messages reliably.

The only radio system that could reach deeply submerged submarines at operational depth. ELF required massive infrastructure — the US system used 84 miles of buried antenna cable grounded into bedrock. Extremely low data rates meant only short coded messages (typically three-letter groups) could be sent, usually ordering the submarine to come to shallower depth for VLF reception. The US decommissioned its ELF system in 2004.

HF radio provides two-way communication but requires the submarine to surface or raise a mast above water. HF signals bounce off the ionosphere, enabling global range. Modern HF systems use frequency-hopping and burst transmission to minimize exposure time. Submarines use HF for detailed message traffic, intelligence updates, and operational orders when VLF bandwidth is insufficient.

Satellite communication provides the highest bandwidth available to submarines, enabling email, intelligence downloads, video, and real-time chat. Requires raising a small mast above the surface. Modern systems like MUOS (Mobile User Objective System) provide near-global coverage. EHF (Extremely High Frequency) SATCOM offers jam-resistant, encrypted communication for the most sensitive traffic. Submarine exposure time is minimized through burst transmission — compressing and transmitting data in seconds.

A buoyant wire antenna streamed from the submarine at depth, floating near the surface to receive VLF broadcasts. The submarine can remain at 20-30 meters depth while the antenna floats at or near the surface. This is less detectable than raising a mast but creates a potential visual and radar signature on the surface. Modern towed buoy antennas combine VLF reception with GPS updating.

Acoustic signals propagate through water far better than radio waves, enabling direct submarine-to-submarine or submarine-to-surface communication. The AN/WQC-2 underwater telephone provides short-range voice communication. However, acoustic communication reveals the submarine's presence and location, so it is used sparingly — typically for safety (e.g., to communicate with friendly submarines in close proximity) rather than tactical messaging.

How do submarines communicate while submerged?

Submarines use several methods to communicate while submerged, but all involve significant compromises. Very Low Frequency (VLF) radio waves at 3-30 kHz can penetrate seawater to depths of about 20 meters, allowing one-way communication to submarines at periscope or shallow depth. Extremely Low Frequency (ELF) at 3-300 Hz can reach submarines at operational depth but transmits data so slowly that a single three-letter code group takes 15 minutes. Submarines can also deploy trailing wire antennas, towed buoy antennas, or rise to periscope depth to raise a communications mast for satellite or HF radio contact. The fundamental challenge is that seawater is essentially opaque to most electromagnetic radiation, making two-way real-time communication with a deeply submerged submarine extremely difficult.

What is ELF communication and why was it important for submarines?

Extremely Low Frequency (ELF) communication operates at 3-300 Hz and was the only radio technology capable of reaching deeply submerged submarines at operational depths of 100-200 meters or more. The US Navy operated two ELF transmitters — one at Clam Lake, Wisconsin, and another at Republic, Michigan — from 1989 to 2004. The Soviet Union operated a similar system called ZEVS near Murmansk. ELF signals required enormous antennas (the US system used 84 miles of buried cable) and could only transmit extremely simple coded messages at about one character per minute. A typical three-letter message took 15 minutes to send. Despite these limitations, ELF was critical for nuclear deterrence because it could order an SSBN to come to shallower depth to receive more detailed VLF or satellite messages without the submarine ever needing to expose itself.

Can submarines communicate with each other underwater?

Submarines can communicate with each other underwater using underwater acoustic communication (sonar-based messaging), but this is rarely done in practice because transmitting active sonar signals reveals the submarine's position. Underwater telephone systems like the AN/WQC-2 can transmit voice messages at short range using acoustic signals, but again this compromises stealth. In wartime, submarines typically maintain strict radio silence and operate independently according to pre-arranged plans. Some modern navies are developing low-probability-of-intercept (LPI) acoustic communication systems that use spread-spectrum techniques to make transmissions difficult to detect, similar to how spread-spectrum radio works in air. Blue-green laser communication is also being researched for short-range submarine-to-submarine links.

How do submarines receive orders for nuclear missile launch?

Ballistic missile submarines (SSBNs) receive Emergency Action Messages (EAMs) through a carefully layered communication system designed for maximum survivability. The primary method is VLF radio broadcast from shore-based transmitters or TACAMO (Take Charge and Move Out) aircraft — specifically the US Navy's E-6B Mercury aircraft, which trail miles-long wire antennas while orbiting. The message is authenticated using sealed two-person codes stored in a safe aboard the submarine. If VLF is unavailable, ELF provides a backup to reach deeply submerged boats with a simple "come to communications depth" order. The entire system is designed so that a valid launch order can reach an SSBN even if the national command authority and most military infrastructure has been destroyed in a nuclear first strike.

What is TACAMO and how does it work?

TACAMO (Take Charge and Move Out) is the US Navy's airborne communication relay system for transmitting orders to ballistic missile submarines. Currently operated by Fleet Air Reconnaissance Squadron THREE (VQ-3) and VQ-7 using E-6B Mercury aircraft — modified Boeing 707s — TACAMO planes trail a very long wire antenna (up to 26,000 feet / 8 km long) while flying in a tight orbit to keep the antenna as vertical as possible. This creates an effective VLF transmitter that can reach submarines at shallow depth. At least one TACAMO aircraft is airborne at all times, ensuring continuous communication capability with the SSBN fleet. The E-6B also serves as an airborne command post (ABNCP) for launching land-based ICBMs if ground-based launch control centers are destroyed.

Is laser communication the future of submarine communications?

Blue-green laser communication (wavelengths of 450-550 nm) is one of the most promising technologies for future submarine communications because seawater is relatively transparent to blue-green light. Satellite-based blue-green lasers could theoretically communicate with submarines at depths of up to 200 meters at much higher data rates than ELF or VLF. However, significant challenges remain: ocean turbidity, biological interference, precise beam pointing from satellite to submarine, cloud cover blocking the laser, and the need for the submarine to have upward-facing optical receivers. Several nations including the US, China, and Russia are actively researching this technology. China has reportedly made significant progress in satellite-to-submarine laser communication experiments, though operational systems remain years away.