At a speed of 12 knots, a 1 degree variation in heading will produce a lateral speed of around 20 feet per minute. For this reason, experienced and qualified helmsmen are required during the replenishment, and the crew on the bridge must give their undivided attention to the ship's course and speed. The risk is increased when a replenishment ship is servicing two ships at once. In case of emergency, crews practice emergency breakaway procedures, where the ships will separate in less-than-optimal situations. Although the ships will be saved from collision, it is possible to lose stores, as the ships may not be able to finish the current transfer. Following successful completion of replenishment, many US ships engage in the custom of playing a signature tune over the replenished vessel's PA system as they break away from the supplying vessel. In the Royal Australian Navy it is customary for ships to fly a special flag during the RAS operation, distinctive to each ship. As many ships are named for Australian towns and cities, it is often the case that they fly flags of AFL, NRL or A-League teams associated with that town or city. The flying of flags popularising brands of beer or other alcoholic beverages is also not uncommon. The earliest type of replenishment, rarely used today, is "astern fueling". In this method, the receiving ship follows directly behind the supplying ship. The fuel-supplying ship throws a marker buoy into the sea and the receiving ship takes station with it. Then the delivering ship trails a hose in the water that the fuel-receiving ship retrieves and connects to. This method is more limited, as only one transfer rig can be set up. However, it is safer, as a slight course error will not cause a collision. US Navy experiments with "Cuyama" and led the Navy to conclude that the rate of fuel transfer was too slow to be useful. But the astern method of refuelling was used by the German and Japanese Navies during World War II; and this method was still used by the Soviet navy for many decades thereafter. A third type of underway replenishment is "vertical replenishment" (VERTREP). In this method, a helicopter lifts cargo from the supplying ship and lowers it to the receiving ship. The main advantage of this method is that the ships do not need to be close to each other, so there is little risk of collision; VERTREP is also used to supplement and speed stores transfer between ships conducting CONREP. However, the maximum load and transfer speeds are both limited by the capacity of the helicopter, and fuel and other liquids cannot be supplied via VERTREP.