Based on current and past success, the Colombian Marines are seeking to expand, adding more troops to the current force of four brigades (one amphibious assault and four riverine.) But given the declining strength of the enemy (drug gangs and leftist rebels), and resistance from the army, it's unlikely to happen. The strength of the marine force will stay at 35,000.
The success of the Colombian marines is largely attributable to a close relationship with the U.S. Marine Corps over the last two decades. This led to adopting very high standards for training recruits (via an intense 13 week boot camp) and selecting and training NCOs and officers. This, plus years of combat experience, have made Colombian marines the most effective amphibious units in the world.
The first Colombian naval infantry battalions were raised in 1940. At the time, they were simply what the name implied; sailors trained to serve as ground combat troops. After World War II, Colombian naval infantry established a professional relationship with the U.S. Marine Corps that grew decade by decade. By the 1990s, the U.S. Marines came to consider the Colombian marines their peers.
The marines have been particularly effective on the rivers and along the coasts. The decades-long war against leftist rebels and cocaine cartels has moved to the coasts, as the Colombian security forces chase the gangs out of their inland sanctuaries. The big chore now is trying to halt the export of cocaine.
Although the larger (250,000 troops) army has many elite units, the entire Colombian Marine Infantry force is considered above average in terms of effectiveness and reliability. Since most of the existing brigades have years of experience operating along rivers and coasts, the force has a large number of troops experienced in these types of operations. The marine argument for expansion was that more riverine units could shut down the drug smuggling and keep it down. But politicians saw an expanded, and successful, marine force becoming difficult (because marines have a good public image) to reduce to a more affordable size later on. Colombian politicians note that this has been the experience in the United States, and don't want to repeat it.