How far does that field travel, though, and how much does it affect the field that a submarine has by nature? Remember, a submarine has somewhere in the range o

How far does that field travel, though, and how much does it affect the field that a submarine has by nature? Remember, a submarine has somewhere in the range of 6-12 inches or more of special types of steel for their inner pressure hulls, so that gives off a pretty freakin' big magnetic signature anyways. Generally, there aren't any super-reliable ways to track a sub from more than a few kilometers anyways, and those are mostly acoustic, so you want to reduce the acoustic signature way way more than the magnetic signature. A magnetic anomaly detector will generally just give you a "hot/cold" signal, as in the "you're getting hotter/colder" game you play as a kid, and "hot" here means "there might be a sub within the nearby few kilometers, but it could also be an unmapped underwater mountain full of iron or a cargo ship we can't see right now".