ALT Smuggling inside shipping containers aboard boats carrying licit cargo. No estimates exist for how many tons of cocaine are smuggled this way each year, because it is impossible to know what has gone undetected. However, large-scale container seizures have become more frequent in recent years, especially at European ports.[236] Submarines and semi-submersible craft. These have larger payloads than small boats and are harder to detect. Authorities in Colombia and Ecuador periodically raid sites, often hidden in dense Pacific mangrove estuaries, where traffickers build these vessels.[237] Small boats making short hops up the coasts of South and Central America. This is more time-consuming than using the open ocean and probably requires paying off more corrupt authorities along the way. However, it involves less time in international waters and is less vulnerable to interdiction, lethal or otherwise, from U.S. forces. Overland transshipment, usually along road networks, perhaps combined w