Germany used bicycles again in World War II, while the British employed airborne "Cycle-commandos" with folding bikes. In the Vietnam War, communist forces used bicycles extensively as cargo carriers along the Ho Chi Minh Trail. The last country known to maintain a regiment of bicycle troops was Switzerland, which disbanded its last unit in 2003. Two broad and correlated themes run in bicycle activism: one is about advocating the bicycle as an alternative mode of transport, and the other is about the creation of conditions to permit and/or encourage bicycle use, both for utility and recreational cycling. Although the first, which emphasizes the potential for energy and resource conservation and health benefits gained from cycling versus automobile use, is relatively undisputed, the second is the subject of much debate. It is generally agreed that improved local and inter-city rail services and other methods of mass transportation (including greater provision for cycle carriage on such services) create conditions to encourage bicycle use. However, there are different opinions on the role of various types of cycling infrastructure in building bicycle-friendly cities and roads. Some bicycle activists (including some traffic management advisers) seek the construction of bike paths, cycle tracks and bike lanes for journeys of all lengths and point to their success in promoting safety and encouraging more people to cycle. Some activists, especially those from the vehicular cycling tradition, view the safety, practicality, and intent of such facilities with suspicion. They favor a more holistic approach based on the 4 'E's; "education" (of everyone involved), "encouragement" (to apply the education), "enforcement" (to protect the rights of others), and "engineering" (to facilitate travel while respecting every person's equal right to do so). Some groups offer training courses to help cyclists integrate themselves with other traffic. Critical Mass is an event typically held on the last Friday of every month in cities around the world where bicyclists take to the streets "en masse". While the ride was founded with the idea of drawing attention to how unfriendly the city was to bicyclists, the leaderless structure of Critical Mass makes it impossible to assign it any one specific goal. In fact, the purpose of Critical Mass is not formalized beyond the direct action of meeting at a set location and time and traveling as a group through city streets. There is a long-running cycle helmet debate among activists. The most heated controversy surrounds the topic of compulsory helmet use. Cyclists form associations, both for specific interests (trails development, road maintenance, bike maintenance, urban design, racing clubs, touring clubs, etc.) and for more global goals (energy conservation, pollution reduction, promotion of fitness).