I'm learning Japanese, so I've been reading an action story to practice.
A scientist sends a pen drive to the news in order to expose some terrorists that were misusing his research for war purposes. The news makes a report about the theoretical assessments of his research, but the scientist is confused because the data on the pen drive was different.
兵器転用の内容、だったはずだ。
From what I can understand, 兵器転用 is something like "weaponization" but I'm not sure.
兵器 just means war weapon, and 転用 means (re-)using something for another purpose. In this context, 内容 refers to the content of the data in the drive.
So the sentence in question is essentially the same as 兵器へ転用するという内容だったはずだ ("I believe the data was about using my research for weapons"). 兵器転用 is not a common compound listed in dictionaries, but there is no particle between 兵器 and 転用 because this is the exact topic of the current story, and the speaker thinks it can be treated almost like a set phrase. Therefore, 'weaponization' seems to be a good translation to me.
Related: the omission of an implied "の" creates the appearance of a 四字熟語{よじじゅくご}?
