Hello Aspirant,
As we know that Marcos is one of the branch of indian navy .so if anyone who wants to join Marcos he have to join indian navy . At first place to become a Marcos the candidate should be a good swimmer. The candidate should swim at least 300mtr. And should have a good physical strength . A Marcos commandos Own the golden diver badged which indicate that he is a diver that means before becoming a Marcos you have to pass the diving tests and own the diver badge and to become a diver once again you should  be a good swimmer and very few candidates pass the diving test . Also after becoming a diver you'll get increment in your salary . Therefore to become a Marcos you should  have a good physical strength and also be a good swimmer. A lot of emphasis and focus should be given on the physical training because it is on you how much you can suffer... and the trainer will not let you out but candidates by there own leave the training Because they are physically mentally torched .

All the very best.. Work hard and serve the nation with proud..