https://www.news.com.au/travel/travel-updates/incidents/us-navy-detected-titan-sub-implosion-with-top-secret-acoustic-system-the-day-vessel-went-missing/news-story/d981b119dda6b4325a2e9957ecd12a7c

Same deal with MH370 going missing -- The big countries would have known exactly where it went down but didn't want to reveal their capabilities.