Pre-war U-boats had the following features –

- the U-boat number (without the U) was painted in large numerals approximately 1.5 metres tall on both sides of the conning tower. Any U-boat photographed without this number is therefore a wartime boat.
- a small oval plate inscribed with the U-boat’s number (with the U) was located just under the small free-flooding holes near to the bow, on both sides of the hull.
- an unpainted bronze eagle plaque was located on the front face of the tower, just below the wind deflector.
- the raised detail of the circle and square markers, both of which had crosses within them, were sometimes painted black. In other case they remained grey, while sometimes the background of the marker (the four squares within the larger square and the four squares within the circle) was painted white. These markers indicated the location of compressed air connections, and were found on both port and starboard walls of the tower. The raised detail of the square marker with a cross within it on either side of the magnetic compass housing was painted similarly. These markers indicated the location of connections to fill air bottles.
- the emergency rescue buoy, two of which were in place on U-boat decks, were red and white. On Type VIIs, the first was located forward of the 20mm Flak gun and the second was just aft of the capstan. Some of these red and white buoys had three white strips which curved in a circular pattern around the outside. Black text appeared upon these strips; the topmost strip read “Unterseeboot” followed by the U-boat’s number.
- sometimes during the pre-war years the red horseshoe-shaped lifebelts would have the name of the U-boat’s flotilla and the U-boat’s number marked in large white letters and numerals.

Just prior to the start of the hostilities the first three features were all removed, and the circles and squares with the crosses within were painted the same grey as the conning tower. Most of the emergency rescue buoys were moved inside metal deck hatches so they would be less obstructive to the crews working on the deck. On the wartime U-boats which retained these buoys, they were painted black rather than red and white.

During the pre-war years it was common to see U-boats sporting different colours to others in the harbour, since different schemes were being tried at this time. It is possible to determine their colours because in pre-war times several U-boats were often photographed next to their tenders. The Dunkelgrau 51 hulls and Hellgrau 50 superstructures of the tenders provide reference points which allow comparisons to be made.

Some of the earliest pre-war U-boat schemes included –

Dunkelgrau 51 upper hulls and Dunkelgrau 51 towers, with the numbers on the tower in white.
Dunkelgrau 51 upper hulls and white towers, with the numbers on the tower in dark grey.
Dunkelgrau 52 upper hulls and white towers, with the numbers on the tower in dark grey (rare).
Hellgrau 50 upper hulls and Hellgrau 50 towers, with the numbers on the tower in dark grey.

Later on a very dark grey colour that is likely to have been Dunkelgrau 52 was used on the upper hulls and towers. Then, immediately prior to the war, the most common scheme within the U-boat fleet consisted of Dunkelgrau 51 on the upper hulls and towers. In both these latter two cases, the numbers on the conning towers were in white.