With Spring Training fast approaching, MLB.com will take a look at a different aspect of this year's Mariners squad each day this week. Today's topic: What's the vision?SEATTLE -- Since general manager Jerry Dipoto took over the Mariners' reins at the end of the 2015 season, his mission has been

With Spring Training fast approaching, MLB.com will take a look at a different aspect of this year's Mariners squad each day this week. Today's topic: What's the vision?

SEATTLE -- Since general manager Jerry Dipoto took over the Mariners' reins at the end of the 2015 season, his mission has been crystal clear.

With a well-paid veteran nucleus already in place, Dipoto identified Robinson Cano , Felix Hernandez , Nelson Cruz and Kyle Seager as his "Core Four" and proceeded to implement a plan to improve the roster around that group by adding players who better fit his vision of what it would take to succeed in Safeco Field.

Dipoto wanted more athletic outfielders, better defenders, some speed to complement the power, a group of hitters focused more toward on-base percentage and pitchers who threw strikes and fit his "control-the-zone" philosophy.

Now 16 months later, the energetic GM has engineered 38 trades and signed six Major League free agents. Of those on the 40-man roster headed to camp next week, only eight were on the 40-man group he inherited from Jack Zduriencik in October 2015.

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"We maintained what we think are the good parts of our team," Dipoto said, "and this was kind of an inevitable reality, more change, although I couldn't have told you it was going to be as broad as it's been."

Many of Dipoto's moves have been relatively minor deals designed to improve the depth, find players who better fit his model or add roster flexibility in some way. But several of the 12 trades he has made this offseason have altered the Mariners' makeup significantly from last year's 86-76 squad.

The additions of shortstop Jean Segura and outfielders Jarrod Dyson and Mitch Haniger bring considerable speed and defense to a team that finished third in the American League in scoring last year and second in home runs, but struggled on the bases and with the gloves.

Carlos Ruiz arrives as a needed veteran presence and offensive threat behind starting catcher Mike Zunino. First baseman Danny Valencia adds a solid right-handed bat to a lineup that has been lefty heavy in recent years.

And a pitching staff that finished third in the AL in ERA last year got deeper with deals for Drew Smyly, Yovani Gallardo and youngsters Rob Whalen , Max Povse , Chris Heston and Dillon Overton , as well as bullpen pieces Marc Rzepczynski , Shae Simmons , James Pazos and Casey Fien .

Dipoto says he's in "win-now" mode in building around his nucleus, but he's also working with the long term in mind by adding in younger players Segura, Haniger, Ben Gamel and Daniel Vogelbach . Second-year manager Scott Servais faces the challenge of molding the newcomers together, but welcomes the improved athleticism, speed and energy of the youthful additions.

"We wanted to get more athletic, we wanted to get better defensively and on the bases and we needed to get younger," Dipoto said. "Last year we had the oldest position player club in baseball and that's an irrefutable fact. Effectively what we've done is we've tried to incorporate a couple of younger players and fold them in without burdening them too much with having to be the centerpiece to what we're doing."

In other words, building up the floor around the core, as Dipoto likes to say, and adding some long-term pieces to the structure as well.

"It's no fun to win if you can't figure out how to sustain, so we're trying to figure that out as we go," he said. "We will make mistakes. It happens when you make [38] trades in a brief period. But as Scott said last year, 'You pick up and you move on.'"

With this Mariners roster, there has been plenty of movement. But Dipoto and Servais believe the team is headed in the right direction. And if their vision is correct, the playoffs could finally be in sight once again at Safeco Field.

Greg Johns has covered the Mariners since 1997, and for MLB.com since 2011. Follow him on Twitter [ @GregJohnsMLB]() and listen to his podcast.