Videos on cryptocurrency using images of billionaire businessman Elon Musk appeared on the YouTube channel.
The Twitter feed appeared to retweet several posts related to NFTs - a type of electronic artwork for investment.
The Army confirmed the "breach", saying it took information security "extremely seriously" and was resolving the issue. Both accounts have now been restored.
An Army spokesperson added: "Whilst we have now resolved the issue an investigation is ongoing and it would be inappropriate to comment further."
It is not clear who is behind the hacking incidents, which also saw the accounts renamed.