And the Blues boss insisted the reason there weren’t further recruits as the transfer window came to a close, was because he didn’t see value in completing other business.
O’Brien’s capture from Sunderland until the campaign received a muted response from many supporters hoping for a high-profile attacking name to arrive on longer terms.
Cowley thought it was an impressive piece of business for Pompey to complete as other avenues hit a dead end.
That was the case with midfielder Lewis Wing, who eventually joined League One rivals Wycombe Wanderers.
And no deal could be completed for Rotherham’s Jamie Lindsay, with the leaders unwilling to leave themselves short of options in the middle of the park.
Cowley explained how he felt the best course of action was to make decisions with an eye on he future.
He said: ‘We would have love to have signed one or two young players in this window, but we couldn’t see good value - the value we wanted.
‘That’s often the case in January.
‘We were all clear we wanted to work with 21 (players), it just wasn’t possible.
‘When you can’t find that value, what you have to do is make some short-term decisions and wait for the value in the next window.
‘That can be frustrating.
‘I get why fans are frustrated. We lost on deadline day and we weren’t able to able to sign the 21st player – then a player in that area gets injured.
‘But we’ve done brilliantly to convince Aiden O’Brien on a short-term deal. Brilliantly.
‘We made a collective decision that (make longer-term decisions) was what we’re going to do in the next window.’
With deadline-day decisions being made with a view to longer-term signings being made in the summer, Cowley looks like to revisit some of the players he was considering at the end of the campaign.
Wing’s Wycombe deal runs only until the summer while Lindsay’s contract also comes to a close, although Rotherham have an option on the Scot to extend his stay at the New York Stadium by another 12 months.
Cowley said: ‘What we want to do is sign players who are on an upward curve.
‘To do that, we then have to use some transfer fees to attract these young players.
‘Then we need the provisions in place to develop those players. That is so vital.’
A message from the Editor, Mark Waldron
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