Why are the officer corps so important in revolutions and coups? What do they need to pull off a success?

The officer corps tend to be important in revolutions and coups for a couple reasons: 

• first, they tend to have more cultural capital than the rank-and-file, which means that they tend to be more plugged in to political ideas (which is necessary for perceiving poor conditions as injustice) and political movements (which are important for coordination). They also tend to have a higher socioeconomic status, which means that they feel that they deserve a political voice.
• second, as I discussed before, the rank-and-file spend a good part of their training learning to obey orders from their officers, and looking to them for guidance. This means that when a crisis happens, if the officer corps says “crush the rebels” or “don’t join the rebels,” the rank-and-file tends to do just that, often to the great disappointment of the rebels. (See the June Days of 1848, or the June Rebellion of 1832 that inspired Les Miserables.) On the other hand, if the officer corps says “don’t fire on the protest” or “we’re going to overthrow the monarchy in the name of the people,” they also tend to obey. This is why it’s very stupid to do things that antagonize them, like when Charles X dissolved the National Guard in 1827 but forgot to take their weapons…