Service connection requires an in-service event, and your service treatment records (STRs) are the first place the VA looks for it. When they document the injury or illness, half your battle is already won. When they are silent, you have to explain why.
When the records support you
An STR entry showing the injury, complaint, or treatment is powerful direct evidence of the in-service event. Find those entries and put them front and center.
When they are silent or missing
Plenty of veterans never reported an injury — you toughed it out, or reporting felt like weakness. Records also get lost, and some were destroyed in archive fires. The absence of a record is not proof the event did not happen. Buddy statements, personnel records, unit histories, and your own credible account can rebuild the timeline.
A silent STR is a challenge, not a dead end. We work around it constantly.