Sailing Directions are published in two main parts: Planning Guides and Enroute volumes. The Planning Guides cover voyage planning material—overview of regions, recommended routes, pilotage considerations, and general coastwide features—while the Enroute volumes provide detailed navigation information for specific coastal areas, including approaches, hazards, currents, tides, and port entries. The combination of five Planning Guides and 37 Enroute volumes reflects how this publication group is structured for both planning ahead and navigating step by step along coastlines. Other publication groups serve different purposes and don’t follow this Planning Guide plus Enroute split, which is why they don’t fit the given description. Therefore, the group described is Sailing Directions.

Loran-C was the system that the US Coast Guard terminated in 2010. It’s a long-range radio navigation method that works by using signals from a network of land-based transmitters; receivers measure the timing differences of those signals to determine position. It served for many years, but keeping the transmitter chains ongoing is costly and the accuracy is not as high or as globally reliable as GPS. As GPS became the standard with global coverage, higher precision, and simpler equipment, the Coast Guard phased out Loran-C in 2010. Since then, Loran-C is no longer in active use by the USCG, though the idea of a backup eLoran has been discussed in other regions.

A loxodrome is navigated by maintaining a constant compass bearing as you cross meridians. This means you steer one course and keep the same heading relative to true north throughout the voyage. On a globe, keeping a fixed bearing creates a rhumb line, which appears as a curve that spirals toward the poles because meridians converge while your bearing stays unchanged. This is different from a great-circle path, where the route is the shortest distance between two points but the bearing changes along the way. So, to follow a loxodrome, you simply keep a constant bearing.

Digits 3 through 5 in a 5-digit chart designation are used to pinpoint a specific location within the broader area defined by the leading digits. The first two digits set the larger region or block, while the trailing three digits narrow it down to a precise spot within that region. That makes the trailing digits indicate the exact location you’re looking at on the chart, rather than a general area or subregion. So, the correct interpretation is that the trailing digits correspond to the specific location.