The Hammers were one of the busiest clubs on deadline day, and indeed all summer, signing 12 players in total with a net spend of around £25-30 million including loan fees.
The east Londoners are widely considered to have done some of the best business of the summer overall.
Before the transfer window slammed shut Slaven Bilic bolstered his squad by bringing in Hull City striker Nikica Jelavic, Barcelona midfielder Alex Song, Chelsea star Victor Moses and Nottingham Forest's exciting and powerful winger Michail Antonio.
Supporters have been impressed with the majority of West Ham's signings.
But the deal to bring in former Croatia forward Jelavic – who was playing in the Championship with Hull and at 30 is the oldest recruit of the summer – was one which sparked criticism from fans.
Many feel the club needed a better quality and younger striker given Andy Carroll's persistent injury problems and the over reliance on Diafra Sakho.
'He solves our striking problems'
But speaking to West Ham's official website, Jack has defended the club's decision to bring in Jelavic and says he can be of benefit even when he isn't playing.
"We solved our striking problems by bringing in Nikica Jelavic and Slaven was keen to bring him to the club," Jack told whufc.com.
"The manager knows everything about him and he has scored goals in the Premier League before.
"He will put more pressure on Sakho and Carroll and give us real competition for places in the forward line.
"I'm sure there a lot of clubs in the top flight that would have liked to have signed him."
Does young Jack make a valid point?
While young Jack's reassurances over Jelavic may not hold much water with some West Ham fans, he does make some valid points.
There is no denying the former Everton striker's statistics stand up to scrutiny.
He is believed to have cost the Hammers around £3 million – as reported by the likes of BBC Sport – and at 30-years-old should still have at least two or three years left in him at the top level.
His goal record across his entire career is almost exactly one in three.
He has 104 goals from 314 career matches for club and country, 30 of which were scored in the Premier League during spells at Everton and Hull.
Croatian connection can help
Jelavic has already told West Ham's official website how much he is looking forward to working with his old Hadjuk Split and international boss Bilic again, describing him as 'a great manager and a great man'.
Hammers fans are expecting him to be nothing more than a squad player, particularly when Carroll, Enner Valencia and Mauro Zarate are all fit.
But the Hammers faithful also love an underdog and the former Rangers striker could yet surprise a few by cementing his place as a key player in what is the last ever season at the Boleyn Ground.