Naval Academy tactics section commander Lieutenant Senior Grade Ott Laanemets says based on what is known right now about the apparent chase for a Russian submarine in Swedish waters, nothing can be ruled out.
But he suggested that the ships being used for the search indicated that they may be looking for an unmanned craft.
"They have said that it is of foreign origin and that it is not of biological origin. It could be a submarine, but it could be something else, something smaller," Laanemets said on ETV.
His opinion was shared by retired Vice Admiral Tarmo Kõuts, former head of the Estonian Defense Forces, in similar comments.
In brief, Laanemets said, it could be a robot or, despite the above claims, it could be brigade of divers or subversives.
"The small islets of eastern Sweden are tight quarters for a submarine. If we look at Estonia's western archipelago, it is shallow and constricted. The waters around the granite rock islands of Sweden are a bit deeper, but it is still quite narrow. A submarine can't rely on the usual submerge and hide tactics there."
Robot submarines, he said, were usually half a meter to three meters in length, he said, and noted that a minesweeper had been searching all day long on Saturday.
"It's meant for finding mines measuring half to two meters in length," said Laanemets.
The search has been going on this weekend in the Kanholmsfjärden area, just a few dozen kilometers from Stockholm.
Foreign Minister Urmas Paet commented briefly on the situation in Postimees, saying that Estonia would refrain from making a statement until more was known; he said that naval vessel traffic on the Baltic Sea had increased in the past year and that the situation was "of course tense."