The most notable of these minor league call-ups was prized prospect Anthony Rendon.
But which Nationals prospects could be among the September call-ups?
Here are are the five Nationals prospects who can most impact the roster during a late season push for the MLB playoffs.
Note: All statistics updated through May 10 courtesy MLB.com unless noted otherwise.
Corey Brown has been called up to the Nationals before. Over the course of the 2011 and 2012 seasons, Brown played a total of 22 games with the Nats.
The Tampa native collected five hits in 28 at-bats with two doubles, one home run, three RBI and four runs scored.
On defense, the athletic outfielder played seven games in left field and two each in center and right, although he is a natural center fielder. He was perfect in 14 total chances at the major league level.
Brown is currently playing for the Syracuse Chiefs in Triple-A. But in September, he would give Davey Johnson more outfield options off his bench, especially if Roger Bernadina's struggles continue. And Brown provides a little more pop at the plate than fellow outfielder and minor leaguer Eury Perez with comparable speed.
Like Corey Brown, Cole Kimball has already seen some action with the Nationals. In 2011, Kimball appeared in 12 games with the Nats. He compiled a 1-0 record and a 1.93 ERA with 11 strikeouts and 11 walks over 14.0 innings pitched.
When MLB teams expand their rosters in September, the bullpens benefit the most. This 6'3", 240-pound right-handed reliever would be a welcome addition, and his major league experience would be a plus.
Of course, to be activated in September, Kimball will have to get healthy. He has yet to pitch a game this season for Triple-A Syracuse. And that's too bad for the Nationals. If he were healthy, Kimball could conceivably be called up right now in an effort to breathe life into a less-than-stellar bullpen.
Jhonatan Solano can be a valuable fill-in at catcher for the Washington Nationals' playoff push to help Wilson Ramos or Kurt Suzuki deal with the occupational hazards of playing catcher at the major league level. Solano has already fulfilled this duty twice since the beginning of the 2012 season.
The 27-year-old Colombia native played 12 games for the Nats in 2012 and three games so far this season before returning to Triple-A Syracuse. In his 41 MLB at-bats to date, Solano has 12 hits, three double, two home runs, six RBI and six runs scored.
Defensively, Solano has been excellent in the limited action he has seen. He has a perfect 1.000 fielding percentage in 73 total chances over 97.1 innings. The man affectionately known as "Onion" has a range factor of 6.08 and has thrown out three of six attempted base stealers.
Nate Karns is the only player on this list who has yet to see any MLB action, let alone with the Washington Nationals.
Karns is ranked 14th among the Nationals' top 20 prospects and is fifth among the nine pitchers on that list. The 25-year-old Pennsylvania native is currently playing at Double-A Harrisburg and is a starting pitcher by trade. In six starts this season, Karms has a 3.03 ERA, 40 strikeouts, 14 walks and a .191 opponents batting average in 32.2 innings pitched.
But according to BaseballProspectNation.com, Karns' strengths and weaknesses as a pitcher may make him more suitable as a reliever:
Fastball-curveball combination could play extremely well at the big league level. Both are plus pitches in the end...Control and command lag behind...Could succeed as a #4 [starter] on the back of the [fastball]-[curveball] combo, or could move to late-inning relief role where the lack of a third pitch and marginal [control and command] can work. Big league profile isn’t in question, just a matter of the role.
Karns has the stuff to help the Nats bullpen, and his experience as a starter could make him very valuable as a long man.
The Washington Nationals have ended the Anthony Rendon experiment.
When Rendon was called up on April 20, he knew that he would play with the big club only as long as Ryan Zimmerman was on the 15-day disabled list. Zimmerman returned to action on May 3, and Rendon returned to Double-A Harrisburg the same day (via the Washington Post)
While with the Nationals, Rendon had six hits in 25 at-bats with one double, one RBI and two runs scored.
Along with collecting some career milestones—first hit, first RBI, first multi-hit game—Rendon gained some Indispensable knowledge about what it takes to succeed at the major league level (via Jon Cooper of MLB.com):
The game is just played a lot smarter up here. Everyone is pretty much on the same level talent-wise but the way the game is played, they'll pitch this pitch instead of that pitch or they'll take something off or they'll play this position over on this hitter. They just play a lot smarter up here. It's going to make a great difference if I do happen to come back. The comfort level is going to be a lot higher now. Obviously, the more things that you do, the more ABs you get, the more times you play, you get more comfortable at it. It helped a lot.
Not if, but when Rendon returns to the Nationals, he will be a smarter baseball player. He's already a very talented one. And the Nationals will welcome him back with open arms for a strong push to the postseason.