With the winter transfer window now open, clubs will be looking to strengthen as they head into the second half of the season. 

Chelsea and Everton have already made key movements - with the former welcoming the already announced transfer of Australian international Sam Kerr, while Everton recently announced the signing of Izzy Christiansen from Lyon.  

With a huge second half of the WSL to come both at the top and bottom end of the table, we look back on some key summer transfers who have made notable impacts at their respective clubs so far this season. 

Esme Morgan

It's been over a year since Willie Kirk was announced as the new manager of Everton, leaving his role as an assistant coach at Manchester United. The Scotsman has completely transformed his Everton side from a team who were fighting relegation last season to a team competing for top four this season. As fellow Scotsman, Sir Alex Ferguson once said, "attack wins you games, defence wins you titles," and while Everton won't be challenging for the title this season at least, the transformation at the back is telling.

The loan signing of Esme Morgan from Manchester City is at the heart of Kirk's defence and has shown to be key in seeing out games - she's even managed a goal in her eight appearances. Last season Everton kept just three clean sheets, a tally that Kirk and his side have already equalled halfway through the season. If Everton wants to continue their brilliant resurgence and aim for a top-four finish, Morgan will be crucial - and it wouldn't come as a surprise if Everton test Manchester City's resolve at the end of the season for a permanent transfer.

 Ebony Salmon

Salmon quickly fell out of favour at Manchester United despite never really getting an opportunity to showcase her talent - spending half of her only season there out on loan to Sheffield United where she scored seven goals in nine appearances in the league.

Her impressive stint on loan earned her a move to the Super League, joining up with Bristol City. Bristol has struggled to find their feet this season and Salmon has been a bright spark among an otherwise lacklustre opening half to their campaign. The 18-year-old has generally made her appearances off the bench but has also earned four starts - scoring 2 goals and recording one assist in the process. Her lightning-quick pace makes her difficult to deal with but her intelligence on and off the ball makes her a cut above. It will be a waste if she doesn't continue to start for Bristol going into the second half of the season as they look to have a relegation battle on their hands.

Hayley Ladd 

It's easy to get caught up in the transfers of relatively big names and that of Jackie Groenen to Manchester United is no different. While her impact has been instant, it mustn't overshadow the arrival of defensive midfielder Hayley Ladd. The Welsh international arrived from Birmingham in the summer and has provided United's backline with the necessary protection, allowing the two midfielders in front of her - often Groenen and Zelem - license to roam forward knowing they're covered. 

Ladd has already shown her versatility early on in her United career, slotting into the backline when called upon, but her presence in the defensive midfield role has been crucial for United's transition into the Super League and will continue to be instrumental in the second half of the season.

Winter transfers 

Clubs will be hoping any transfers brought in during the January window will have equally as big of an impact - including Kerr helping Chelsea compete with Arsenal and City for the title. 

Liverpool also recently announced the signing of forward Rachel Furness from Reading - someone who will be able to help them score much-needed goals as they fight to stay in the top flight following their poor first half of the season. 

The winter transfer window will close January 23rd, with Super League action resuming January 5th.